Name: synthesis and characterization of supramolecular colloids
Uploaded: 2016-04-22T14:00:00.000+00:00
Duration: 9 min 26 s
Description: Watch this Scientific Journal Video about Synthesis and Characterization of Supramolecular Colloids at JoVE.com

The authors acknowledge The Netherlands Organization for Scientific research (NWO ECHO-STIP Grant 717.013.005, NWO VIDI Grant 723.014.006) for the financial support.

1. Synthesis of Core-shell Silica Particles
Note: Silica particles are synthesized according to the following procedure, which is based on the St&#246;ber method24,25.
<ol>
	<li>Synthesis of fluorescent silica seeds
	<ol>
		<li>Dissolve 105 mg (0.27 mmol) of fluorescein-isothiocyanate in 5 ml of ethanol.</li>
		<li>Add 100 &#181;l of (3-aminopropyl) triethoxysilane (APTES, 0.43 mmol) to the previous solution.</li>
		<li>Sonicate the solution during 5 min and let it react overnight under an argon atmosphere at room temperature while stirring. The dye-functionalized APTES complex is used without purification.</li>
		<li>In a 1 L round-bottom flask mix 2.5 ml of the dye-functionalized APTES with 25 ml of ammonia (25% in water) and 250 ml of ethanol.</li>
		<li>Add 10 ml of tetraethylorthosilicate (TEOS) under the meniscus of the previous reaction mixture with the help of a glass pipette while stirring with a magnetic stirrer.</li>
		<li>Similarly, after 5 hr, add another 1.75 ml of TEOS and stir the mixture overnight under an argon atmosphere.</li>
		<li>Pour the dispersion into several 45 ml tubes.</li>
		<li>Centrifuge the tubes (350 x g, 30 min), remove the supernatant and add 30 ml of fresh ethanol in each tube. Sonicate the new dispersions for 3 min, and centrifuge again to remove the supernatant. Repeat these washing steps 3 times.</li>
		<li>Keep the fluorescent seeds in ethanol in a concentration of about 13.6 mg/ml and in the dark (avoid exposure to light).</li>
		<li>Prepare non-fluorescent seeds following the same procedure omitting the addition of the fluorescent dye. 
		Note: Following this procedure, seeds of about 100 nm in radius are obtained.</li>
	</ol>
	</li>
	<li>Synthesis of core-shell silica particles
	<ol>
		<li>Fill a 1 L round-bottom flask with 51 ml of ethanol, 17 ml of deionized water, 3.4 ml of ammonia (25% in water) and 4 ml of the seed dispersion (54.4 mg of fluorescent seeds approximately).</li>
		<li>Fill a plastic syringe with 5 ml of TEOS and 10 ml of ethanol.</li>
		<li>Fill a second plastic syringe with 1.34 ml of ammonia (25% in water), 3.4 ml of deionized water and 10.25 ml of ethanol.</li>
		<li>Connect both syringes to the round-bottom flask with plastic tubing.</li>
		<li>Equip the flask with an argon flow and a magnetic stirrer. The argon inlet has to be next to the outlet of the second syringe to avoid contact between ammonia gases from the TEOS droplets to prevent secondary nucleation.</li>
		<li>Add the content of both syringes at the same time at 1.7 ml/hr using peristaltic pumps while stirring the mixture. Ensure to obtain free falling droplets to avoid gliding on the walls and therefore secondary nucleation.</li>
		<li>Stop the addition after 7 hr to obtain core-shell particles of approximately 300 nm in radius.</li>
		<li>Pour the content of the flask into several 45 ml tubes.</li>
		<li>Centrifuge the tubes (350 x g, 30 min), remove the supernatant and add 30 ml of fresh ethanol in each tube. Sonicate the new dispersion for 3 min, and centrifuge again to remove the supernatant. Repeat these washing steps 3 times.</li>
		<li>Keep the core-shell particles in ethanol and in the dark (avoid exposure to light).</li>
		<li>Prepare non-fluorescent silica particles following the same procedure but using the non-fluorescent seeds.</li>
	</ol>
	</li>
</ol>
2. Functionalization of Silica Colloids
<ol>
	<li>Synthesis of NVOC-functionalized colloids
	<ol>
		<li>Disperse 10 mg of core-shell silica particles in 1 ml of ethanol together with 12 mg (0.03 mmol) of the NVOC-C11-OH molecule and 31 mg (0.11 mmol) of stearyl alcohol in a 50 ml round-bottom flask (resulting in a 20/80 NVOC-C11-OH/stearyl alcohol molar ratio).</li>
		<li>Sonicate the mixture for 10 min to ensure that all molecules are dissolved and the particles are well dispersed.</li>
		<li>Add to the mixture a magnetic stirrer bar and evaporate the ethanol with a steady stream of argon at room temperature. Before proceeding, ensure that there is no ethanol left, otherwise it could react with the silanol groups of the particles. To check whether the ethanol is completely evaporated pay attention to the temperature of the bottom of the flask. If it feels cold, ethanol is not yet completely evaporated.</li>
		<li>Heat the flask up to 180 &#176;C for 6 hr under continuous stirring and under a steady stream of argon22.</li>
		<li>Let the flask cool down to room temperature.</li>
		<li>Add 3 ml of CHCl3 into the flask and sonicate for 5 min (or until all the solid content has been dissolved or dispersed).</li>
		<li>Centrifuge the dispersion (2,600 x g, 4 min), remove the supernatant and add fresh CHCl3. Sonicate the new dispersion for 3 min, and centrifuge again to remove the supernatant. Repeat these washing steps 6 times.</li>
		<li>Dry the particles at 70 &#176;C in vacuo overnight and store them in a desiccator.</li>
	</ol>
	</li>
	<li>Synthesis of BTA-colloids
	<ol>
		<li>Disperse 10 mg of particles functionalized with a 20/80 molar ratio of NVOC-C11-OH/stearyl alcohol in 3 ml of CHCl3.</li>
		<li>Irradiate the dispersion in a UV-oven (&#955;max=354 nm) for 1 hr to cleave the NVOC group. Ensure that the deprotection is homogeneous on the surface of the particles by stirring the dispersion gently with a magnetic stirrer while deprotecting. This yields the amine-functionalized particles (Figure 1a).</li>
		<li>Dissolve 9 mg of the benzene-1,3,5-tricarboxamide derivative (BTA, 0.01 mmol), 8.7 &#181;l of N,N-diisopropylethylamine (DIPEA, 0.05 mmol) and 5.2 mg of (benzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate (PyBOP, 0.01 mmol) in 1 ml of CHCl3.</li>
		<li>Add the solution to the amine- functionalized particle dispersion and stir overnight at room temperature and under an argon atmosphere.</li>
		<li>Centrifuge the dispersion (2,600 x g, 4 min), remove the supernatant and add 3 ml of fresh CHCl3. Sonicate the new dispersion for 3 min, and centrifuge again to remove the supernatant. Repeat these washing steps 6 times.</li>
		<li>Dry the particles at 70 &#176;C in vacuo for 48 hr and store them in a desiccator.</li>
	</ol>
	</li>
</ol>
3. Static Light Scattering Measurements (SLS)
Note: Use non-fluorescent particles, since the fluorescent core absorbs light of the same wavelength as the incident laser light of conventional light scattering equipment.
<ol>
	<li>Functionalize 10 mg of non-fluorescent silica particles with stearyl alcohol only (no NVOC-C11-OH) following the procedure described in section 2.1.</li>
	<li>Prepare 500 &#956;l of a dispersion of 0.033 mg/ml of non-functionalized particles in water and another one of 2 mg/ml of the stearyl alcohol-coated particles in cyclohexane.</li>
	<li>Sonicate both dispersions for at least 20 min to ensure that the particles are well dispersed.</li>
	<li>Measure the scattered intensity of both dispersions, the solvents and the reference solvent from 30&#176; to 120&#176; in steps of 5&#176;.</li>
	<li>Plot the intensity of the sample (Isample) as a function of q 
	(Equation 1) q = 4&#960;nsolventsin(&#952;/2)/&#955;o 
	with the scattering angle &#952;, the refractive index of the solvent nsolvent and the wavelength of the laser &#955;o.</li>
	<li>Fit the data to the following equation using software (e.g., Origin) 
	(Equation 2) Isample = CP(qR) 
	where C is a constant and the form factor P(qR) is given by 
	(Equation 3)<img alt="Equation 3" src="/files/ftp_upload/53934/53934eq3.jpg" /> 
	 
	wherein the average radius of the spherical colloids is R.</li>
	<li>Extract R from the fits for each dispersion.</li>
	<li>Calculate the Rayleigh Ratio (R&#952;), which is an absolute measure for the intensity of the scattered light, according to the following equation, for each &#952;. 
	(Equation 4)<img alt="Equation 4" src="/files/ftp_upload/53934/53934eq4.jpg" />&#160; 
	 
	with the intensity of the sample, the solvent and the reference, Isample, Isolvent and Ireference respectively, the refractive index of the solvent and the reference nsolvent and nreference, correspondingly, and the Rayleigh Ratio of the reference Rreference. Here use toluene as a reference, such that nwater = 1.332, ntoluene = 1.497, ncyclohexane = 1.426; Rtoluene = 2.74x10-3 m-1 26.</li>
	<li>Compute the average refractive index of the colloids (ncolloids) from R&#952; and Equation 5. 
	(Equation 5)<img alt="Equation 5" src="/files/ftp_upload/53934/53934eq5.jpg" />&#160; 
	 
	with the number of particles per volume N, the volume of a particle vparticle given by vparticle =4/3&#960;R3, and assuming that the structure factor S(q)~1, which is the limit of non-interacting particles.</li>
</ol>
4. Quantification of the Number of Active Sites Per Particle
Note: Use small particles of 13 nm in radius (with a larger surface-to-volume ratio).
<ol>
	<li>Functionalize small commercially available particles with a 20/80 molar ratio of NVOC-C11-OH/stearyl alcohol following the procedure described in Section 2.1.</li>
	<li>Disperse 20 mg of the small, functionalized particles in 1 ml CHCl3 and irradiate the dispersion in a UV-oven (&#955;max=354 nm) for 1 hr to cleave the NVOC group. Stir the dispersion gently with a magnetic stirrer bar while deprotecting. In this manner the colloids do not sediment and their surface remains exposed to the UV light, hence ensuring homogeneous deprotection.</li>
	<li>Spin down the resulting amine-functionalized particles (3,400 x g, 10 min) and remove the supernatant.</li>
	<li>Dry the particles at 70 &#176;C for 2 hr.</li>
	<li>Dissolve 0.50 mg of succinimidyl 3-(2-pyridyldithio)propionate (SPDP, 0.0016 mmol) in 200 &#181;l of dimethylformamide (DMF).</li>
	<li>Add the SPDP solution to the 20 mg of the dried amine-functionalized particles and vortex the system for 30 min. Within this time, all available primary amines on the colloids have reacted with the SPDP.</li>
	<li>Wash the particles with 1 ml of DMF for 6 times (or until no free SPDP is detected in the supernatant by UV-Vis spectroscopy at &#955;=375 nm). In the last washing step try to remove as much supernatant as possible.</li>
	<li>Dissolve 0.53 mg of dithiothreitol (DTT, 0.0034 mmol) in 50 &#181;l of DMF. Add the DTT solution to the particles and vortex the dispersion for 30 min. Within this time the pyridine-2-thione group is cleaved.</li>
	<li>Determine the absorbance of the free pyridine-2-thione liberated in the supernatant at &#955;=293 nm with a microvolume UV-Vis spectrophotometer.</li>
	<li>Construct a calibration curve to determine the extinction coefficient &#603; (~12.1x103 M-1cm-1) of the pyridine-2-thione in DMF by measuring the absorbance of a dilution series of different known amounts of SPDP with an excess of DTT.</li>
	<li>Calculate the concentration of pyridine-2-thione, Cp2t, which is cleaved from the particles using the Lambert-Beer law: 
	(Equation 6) Abs = Cp2t &#949; l&#160;&#160;&#160;&#160; 
	with the molar concentration of pyridine-2-thione Cp2t, the extinction coefficient &#603; and the path length l.</li>
	<li>Calculate the number of active sites (amines) per particle with the following equation 
	(Equation 7)<img alt="Equation 7" src="/files/ftp_upload/53934/53934eq7.jpg" />&#160;&#160; &#160; &#160; &#160;&#160; &#160; 
	with the mass of one particle Mparticle that is Mparticle = 4/3&#960;R3&#961;, with &#961;=1.295 g/cm3, the total weighted mass of particles Mtotal (20 mg) and the total volume Vtotal (50 &#181;l). This equation assumes that all available amines react with the SPDP and the DTT reduces all SPDP molecules attached to the particles.</li>
</ol>
5. Monitor Colloidal Assembly by Confocal Microscopy
Note: Use core-shell silica particles (with a fluorescent core and a non-fluorescent shell).
<ol>
	<li>Prepare 400 &#181;l of a dispersion of 0.1 wt% of BTA-functionalized particles in cyclohexane and sonicate the sample for 20 min.</li>
	<li>Irradiate the sample vial in the UV oven (&#955;max = 354 nm) to cleave off the o-nitrobenzyl group of the BTA. Take 25 &#181;l aliquots at different times of irradiation, for example from 0 up to 30 min, to monitor the clustering process.</li>
	<li>Place the different aliquots on different glass slides with the help of a spacer and close the chambers with a cover slip (chamber size is 13 mm diameter &#215; 0.12 mm height). After closing the chamber, turn the cover slip upside down to let the particles sediment and adsorb onto the glass, which facilitates the imaging.</li>
	<li>Take several images of each sample with the confocal microscope as soon as possible after sample preparation for each irradiation time.</li>
</ol>
6. Image Analysis
<ol>
	<li>Quantification of the number of singlets with ImageJ 
	Note: All commands used to write the script are described in the ImageJ manual: 
	http://imagej.nih.gov/ij/docs/guide/user-guide.pdf
	<ol>
		<li>Smooth the confocal images to remove isolated pixels from the edges and fill small holes running the &#34;Smooth&#34; function.</li>
		<li>Given that only the cores are fluorescent, dilate the bright areas until the edge of the particles that belong to the same cluster touch and particles merge. Do this using the &#34;Dilate&#34; filter. With particles with approximately 180 nm shell thickness, and pictures with a resolution of 0.02 &#181;m/pixel, two dilation steps are enough.</li>
		<li>Convert the images into a binary picture running the &#34;Make binary&#34; function.</li>
		<li>Set the scale by running the tool &#34;&#34;Set Scale&#8230;&#34;, distance=1 known=0.02 pixel=1 unit=um&#34;&#34; for pictures taken with a resolution of 0.02 &#181;m/pixel for instance.</li>
		<li>Apply a threshold size to discriminate noise and out-of-focus particles from in-of-focus particles. For instance, with pictures taken with a resolution of 0.02 &#181;m/pixel, all areas smaller than 0.2 pixels are ruled out. Do this using the &#34;Analyze particles&#8230;&#34;, &#34;size=0.2-Infinity&#34; command.</li>
		<li>Create an all.jpg image and an all.txt file with the size of all bright areas in the image (clusters and singlets) by using the commands &#34;&#34;results&#34;, _all.txt&#34;&#34; and &#34;&#34;JPEG&#34;, &#34;all&#34;&#34;.</li>
		<li>Assume that all bright areas between 0.2 and 0.7 pixels in size and with a circularity (circularity = 4 &#960; Area/Perimeter2) between 0.7 and 1.0 are singlets running the command &#34;Analyze particles&#8230;&#34;, &#34;circularity=0.7-1.0&#34;.</li>
		<li>Create a singlets.jpg image and a singlets.txt file with the information of all bright areas that are singlets by using the commands &#34;&#34;results&#34;, _singlets.txt&#34;&#34; and &#34;&#34;JPEG&#34;, &#34;singlets&#34;&#34;.</li>
	</ol>
	</li>
	<li>Process the information with Matlab
	<ol>
		<li>Read the singlet .txt file and calculate the average size of a singlet per picture (Asinglet).</li>
		<li>Use the average size of a singlet to compute the number of particles per cluster (Adoublet=2Asinglet, Atriplet=3Asinglet &#8230;) and the total number of particles in the picture from the other all.txt file.</li>
		<li>Calculate the fraction of particles in singlets for each exposure time: fsinglets = number singlets/total particles</li>
		<li>Calculate the fraction of doublets, triplets, etc.: fdoublets= 2*number of doublets/total particles, etc.</li>
	</ol>
	</li>
</ol>

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Controlled growth reaction and continuous production process.</a> J. Eur. Ceram. Soc. 14 (3), 205-214 (1994).</li><li>Wu, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Correlations+between+the+Rayleigh+ratio+and+the+wavelength+for+toluene+and+benzene.">Correlations between the Rayleigh ratio and the wavelength for toluene and benzene.</a> Chem. Phys. 367 (1), 44-47 (2010).</li></ol>

The authors have nothing to disclose.

When cyclohexane, with a refractive index of 1.426, is used as a solvent to disperse the BTA-colloids, van der Waals interactions are very weak, since the refractive indices of colloids and solvent are nearly the same. Note that the concentration of functionalized colloids used for the SLS experiments in cyclohexane is much higher compared to the bare silica colloids in water. This is necessary to obtain a sufficiently strong scattering due to the low contrast as the refractive indices are almost matched. Trace amounts o...

Mesostructured colloidal materials find widespread application in science and technology, as model systems for fundamental studies on atomic and molecular materials1,2, as photonic materials3,4, as drug delivery systems5,6, as coatings7 and in lithography for surface patterning8,9. Since lyophobic colloids are metastable materials that eventually aggregate irreversibly due to the omnipresent van der Waals interactions, their manipulation into specific target structures is notoriously difficult. Numerous strategies have been developed to control colloidal self-assembly including the use of additives to tune the electrostatic10,11 or depletion interactions12,13, or external triggers such as magnetic14 or electric15 fields. A sophisticated alternative strategy to achieve control over the structure, dynamics and mechanics of these systems is their functionalization with molecules interacting through specific and directional forces. Supramolecular chemistry offers a comprehensive toolbox of small molecules exhibiting site-specific, directional and strong yet reversible interactions, which can be modulated in strength by solvent polarity, temperature and light16. Since their properties have been studied extensively in bulk and in solution, these molecules are attractive candidates to structure soft materials into exotic phases in a predictable manner. Despite the clear potential of such an integrated approach to orchestrate colloidal assembly via supramolecular chemistry, these disciplines have rarely interfaced to tailor the properties of mesostructured colloidal materials17,18.
A solid platform of supramolecular colloids must fulfill three main requirements. Firstly, coupling of the supramolecular moiety should be done under mild-conditions to prevent degradation. Secondly, surface forces at separations larger than direct contact should be dominated by the tethered motifs, which means that uncoated colloids should nearly exclusively interact via excluded-volume interactions. Therefore, the physico-chemical properties of the colloids should be tailored to suppress other interactions inherent in colloidal systems, such as van der Waals or electrostatic forces. Thirdly, characterization should allow for an unequivocal attribution of the assembly to the presence of the supramolecular moieties. To meet these three prerequisites, a robust two-step synthesis of supramolecular colloids was developed (Figure 1a). In a first step, hydrophobic NVOC-functionalized silica particles are prepared for dispersion in cyclohexane. The NVOC group can be easily cleaved, yielding amine-functionalized particles. The high reactivity of amines enables straightforward post-functionalization with the desired supramolecular moiety using a wide range of mild reaction conditions. Herein, we prepare supramolecular colloids by functionalization of silica beads with stearyl alcohol and a benzene-1,3,5-tricarboxamide (BTA) derivative20. The stearyl alcohol plays several important roles: it makes the colloids organophilic and it introduces short-range steric repulsions which aids to reduce the nonspecific interaction between colloids21,22. van der Waals forces are further reduced because of the close match between the refractive index of the colloids and the solvent23. Light-and thermoresponsive short-range attractive surface forces are generated by incorporation of o-nitrobenzyl protected BTAs20. O-nitrobenzyl moiety is a photo-cleavable group that blocks the formation of hydrogen bonds between adjacent BTAs when incorporated on the amides in the discotics (Figure 1b). Upon photocleavage by UV-light, the BTA in solution is able to recognize and interact with identical BTA molecules through a 3-fold hydrogen bond array, with a binding strength that is strongly temperature dependent17. Since the van der Waals attractions are minimal for stearyl coated silica particles in cyclohexane as well as light- and temperature-independent, the observed stimuli-responsive colloidal assembly must be BTA-mediated.
This detailed video demonstrates how to synthesize and characterize supramolecular colloids and how to study their self-assembly upon UV-irradiation by confocal microscopy. In addition, a simple image analysis protocol to distinguish colloidal singlets from clustered colloids and to determine the amount of colloids per clusters is reported. The versatility of the synthetic strategy allows to readily vary particle size, surface coverage as well as the introduced binding moiety, which opens up new avenues for the development of a large family of colloidal building blocks for mesostructured advanced materials.

<table><tbody><tr><td>APTES</td><td>Sigma-Aldrich</td><td></td><td></td></tr><tr><td>FTIC</td><td>Sigma-Aldrich</td><td></td><td></td></tr><tr><td>TEOS</td><td>Sigma-Aldrich</td><td></td><td></td></tr><tr><td>LUDOX AS-40</td><td>Sigma-Aldrich</td><td></td><td>Silica particles of 13 nm in radius</td></tr><tr><td>MilliQ</td><td>---</td><td>---</td><td>18.2 M&amp;Omega;&amp;middot;cm at 25 &amp;deg;C</td></tr><tr><td>Ethanol</td><td>SolvaChrom</td><td></td><td>---</td></tr><tr><td>Ammonia (25% in water)</td><td>Sigma-Aldrich</td><td></td><td>---</td></tr><tr><td>Chloroform</td><td>SolvaChrom</td><td></td><td>---</td></tr><tr><td>Cyclohexane</td><td>Sigma-Aldrich</td><td></td><td>---</td></tr><tr><td>Dimethylformamide (DMF)</td><td>Sigma-Aldrich</td><td></td><td>---</td></tr><tr><td>Stearyl alcohol</td><td>Sigma-Aldrich</td><td></td><td>---</td></tr><tr><td>&lt;em&gt;N,N&lt;/em&gt;-Diisopropylethylamine (DIPEA)</td><td>Sigma-Aldrich</td><td></td><td>---</td></tr><tr><td>Benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate (PyBOP)</td><td>Sigma-Aldrich</td><td></td><td>---</td></tr><tr><td>Succinimidyl 3-(2-pyridyldithio)propionate (SPDP)</td><td>Sigma-Aldrich</td><td></td><td>---</td></tr><tr><td>Dithiothreitol (DTT)&amp;nbsp;</td><td>Sigma-Aldrich</td><td></td><td>---</td></tr><tr><td>NVOC-C11-OH</td><td>Synthesized</td><td>---</td><td>I. de Feijter, 2014 Responsive materials from adaptive supramolecular constructs, Doctoral thesis, Technical University of Eindhoven, The Netherlands</td></tr><tr><td>BTA</td><td>Synthesized</td><td>---</td><td>I. de Feijter, 2014 Responsive materials from adaptive supramolecular constructs, Doctoral thesis, Technical University of Eindhoven, The Netherlands</td></tr><tr><td>Centrifuge</td><td>Thermo Scientific</td><td></td><td>Heraeus Megafuge 1.0</td></tr><tr><td>Ultrasound bath</td><td>VWR</td><td></td><td>Ultrasonic cleaner</td></tr><tr><td>Peristaltic pumps</td><td>Harvard Apparatus</td><td></td><td>PHD Ultra Syringe Pump</td></tr><tr><td>UV-oven</td><td>Luzchem</td><td></td><td>LZC-a V UV reactor equipped with 8x8 UVA light bulbs (&amp;lambda;&lt;sub&gt;max&lt;/sub&gt;=354&amp;nbsp;nm)</td></tr><tr><td>Stirrer-heating plate</td><td>Heidolph</td><td></td><td>MR-Hei Standard&lt;br /&gt;&amp;nbsp;&lt;br /&gt;</td></tr><tr><td colspan="4">[header]</td></tr><tr><td>Light Scattering</td><td>ALV</td><td></td><td>CGS-3 MD-4 compact goniometer system, equipped with a Multiple Tau digital real time correlator (ALV-7004) and a solid-state laser (&amp;lambda;=532 nm, 40 mW)</td></tr><tr><td>UV-Vis spectrophotometer</td><td>Thermo Scientific</td><td></td><td>NanoDrop 1000 Spectrophotometer</td></tr><tr><td>Confocal microscope</td><td>Nikon</td><td></td><td>Ti Eclipse with an argon laser with &amp;lambda;&lt;sub&gt;excitation&lt;/sub&gt;=488&amp;nbsp;nm</td></tr><tr><td>Slide spacers</td><td>Sigma-Aldrich</td><td></td><td>Grace BioLabs Secure seal imaging spacer (1 well, diam. &amp;times; thickness 13 mm &amp;times; 0.12 mm)</td></tr><tr><td>Syringes</td><td>BD Plastipak</td><td></td><td>20 ml syringe</td></tr><tr><td>Plastic tubing</td><td>SCI</td><td>BB31695-PE/5</td><td>Ethylene oxide gas sterilizable micro medical tubing</td></tr><tr><td>Pulsating vortex mixer</td><td>VWR</td><td></td><td>Electrical: 120&amp;nbsp;V, 50/60&amp;nbsp;Hz, 150&amp;nbsp;W Speed Range: 500&amp;ndash;3,000 rpm</td></tr></tbody></table>

synthesis and characterization of supramolecular colloids

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical properties for applications in photonics, drug delivery and coating technology. Here we present a new family of colloidal building blocks, coined supramolecular colloids, whose self-assembly is controlled through surface-functionalization with a benzene-1,3,5-tricarboxamide (BTA) derived supramolecular moiety. Such BTAs interact via directional, strong, yet reversible hydrogen-bonds with other identical BTAs. Herein, a protocol is presented that describes how to couple these BTAs to colloids and how to quantify the number of coupling sites, which determines the multivalency of the supramolecular colloids. Light scattering measurements show that the refractive index of the colloids is almost matched with that of the solvent, which strongly reduces the van der Waals forces between the colloids. Before photo-activation, the colloids remain well dispersed, as the BTAs are equipped with a photo-labile group that blocks the formation of hydrogen-bonds. Controlled deprotection with UV-light activates the short-range hydrogen-bonds between the BTAs, which triggers the colloidal self-assembly. The evolution from the dispersed state to the clustered state is monitored by confocal microscopy. These results are further quantified by image analysis with simple routines using ImageJ and Matlab. This merger of supramolecular chemistry and colloidal science offers a direct route towards light- and thermo-responsive colloidal assembly encoded in the surface-grafted monolayer.

&#160;Given that the two-step procedure used to synthesize the supramolecular colloids (Figure 1a), couples the BTA- derivatives (Figure 1b) in a second step at room temperature and in mild-reaction conditions, its stability is ensured.
<img alt="Figure 1" src="/files/ftp_upload/53934/53934fig1.jpg" /> 
Figure 1. Scheme of the synthesis of supramolecular colloids. A) Coupli...

Watch this Scientific Journal Video about Synthesis and Characterization of Supramolecular Colloids at JoVE.com

Synthesis and Characterization of Supramolecular Colloids

A protocol for the synthesis and characterization of colloids coated with supramolecular moieties is described. These supramolecular colloids undergo self-assembly upon the activation of the hydrogen-bonds between the surface-anchored molecules by UV-light.

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical ...

synthesis-and-characterization-of-supramolecular-colloids

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Anatomy and Physiology

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Fundamentals of Chemistry

Solutions and Colloids

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9.7K Views.  Eindhoven University of Technology. A protocol for the synthesis and characterization of colloids coated with supramolecular moieties is described. These supramolecular colloids undergo self-assembly upon the activation of the hydrogen-bonds between the surface-anchored molecules by UV-light.

Video: Synthesis and Characterization of Supramolecular Colloids

Controlling the Size, Shape and Stability of Supramolecular Polymers in Water

For aqueous based supramolecular polymers, the simultaneous control over shape, size and stability is very difficult1. At the same time, the ability to do so is highly important in view of a number of applications in functional soft matter including electronics, biomedical engineering, and sensors. In the past, successful strategies to control the size and shape of supramolecular polymers typically focused on the use of templates2,3, end cappers4 or selective solvent techniques5. 
Here we disclose a strategy based on self-assembling discotic amphiphiles that leads to the control over stack length and shape of ordered, chiral columnar aggregates. By balancing electrostatic repulsive interactions on the hydrophilic rim and attractive non-covalent forces within the hydrophobic core of the polymerizing building block, we manage to create small and discrete spherical objects6,7. Increasing the salt concentration to screen the charges induces a sphere-to-rod transition. Intriguingly, this transition is expressed in an increase of cooperativity in the temperature-dependent self-assembly mechanism, and more stable aggregates are obtained. 
For our study we select a benzene-1,3,5-tricarboxamide (BTA) core connected to a hydrophilic metal chelate via a hydrophobic, fluorinated L-phenylalanine based spacer (Scheme 1). The metal chelate selected is a Gd(III)-DTPA complex that contains two overall remaining charges per complex and necessarily two counter ions. The one-dimensional growth of the aggregate is directed by &pi;-&pi; stacking and intermolecular hydrogen bonding. However, the electrostatic, repulsive forces that arise from the charges on the Gd(III)-DTPA complex start limiting the one-dimensional growth of the BTA-based discotic once a certain size is reached. At millimolar concentrations the formed aggregate has a spherical shape and a diameter of around 5 nm as inferred from 1H-NMR spectroscopy, small angle X-ray scattering, and cryogenic transmission electron microscopy (cryo-TEM). The strength of the electrostatic repulsive interactions between molecules can be reduced by increasing the salt concentration of the buffered solutions. This screening of the charges induces a transition from spherical aggregates into elongated rods with a length &gt; 25 nm. Cryo-TEM allows to visualise the changes in shape and size. In addition, CD spectroscopy permits to derive the mechanistic details of the self-assembly processes before and after the addition of salt. Importantly, the cooperativity -a key feature that dictates the physical properties of the produced supramolecular polymers- increases dramatically upon screening the electrostatic interactions. This increase in cooperativity results in a significant increase in the molecular weight of the formed supramolecular polymers in water.

The goal of this experiment is to determine and control the size, shape and stability of self-assembled discotic amphiphiles in water. For aqueous based supramolecular polymers such level of control is very difficult. We apply a strategy using both repulsive and attractive interactions. The experimental techniques applied to characterize this system are broadly applicable.

For aqueous based supramolecular polymers, the simultaneous control over shape, size and stability is very difficult1. At the same time, the ability to do ...

Engineering

Confocal Imaging of Confined Quiescent and Flowing Colloid-polymer Mixtures

The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed assembly1-3, drug delivery4, improved hydrocarbon recovery5-7, and flowable electrodes for energy storage8. Suspensions containing fluorescent colloids and non-adsorbing polymers are appealing model systems, as the ratio of the polymer radius of gyration to the particle radius&#160;and concentration of polymer control the range and strength of the interparticle attraction, respectively. By tuning the polymer properties and the volume fraction of the colloids, colloid fluids, fluids of clusters, gels, crystals, and glasses can be obtained9.&#160;Confocal microscopy, a variant of fluorescence microscopy, allows an optically transparent and fluorescent sample to be imaged with high spatial and temporal resolution in three dimensions. In this technique, a small pinhole or slit blocks the emitted fluorescent light from regions of the sample that are outside the focal volume of the microscope optical system. As a result, only a thin section of the sample in the focal plane is imaged. This technique is particularly well suited to probe the structure and dynamics in dense colloidal suspensions at the single-particle scale: the particles are large enough to be resolved using visible light and diffuse slowly enough to be captured at typical scan speeds of commercial confocal systems10. Improvements in scan speeds and analysis algorithms have also enabled quantitative confocal imaging of flowing suspensions11-16,37.&#160;In this paper, we demonstrate confocal microscopy experiments to probe the confined phase behavior and flow properties of colloid-polymer mixtures. We first prepare colloid-polymer mixtures that are density- and refractive-index matched. Next, we report a standard protocol for imaging quiescent dense colloid-polymer mixtures under varying confinement in thin wedge-shaped cells. Finally, we demonstrate a protocol for imaging colloid-polymer mixtures during microchannel flow.

Confocal microscopy is used to image quiescent and flowing colloid-polymer mixtures, which are studied as model systems for attractive suspensions. Image analysis algorithms are used to calculate structural and dynamic metrics for the colloidal particles that measure changes due to geometric confinement.

The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed ...

Using Polystyrene-block-poly(acrylic acid)-coated Metal Nanoparticles as Monomers for Their Homo- and Co-polymerization

We present a template-free method for &#8220;polymerizing&#8221; nanoparticles into long chains without side branches. A variety of nanoparticles are encapsulated in polystyrene-block-poly(acrylic acid) (PSPAA) shells and then used as monomers for their self-assembly. Spherical PSPAA micelles upon acid treatment are known to assemble into cylindrical micelles. Exploiting this tendency, the core-shell nanoparticles are induced to aggregate, coalesce, and then transform into long chains. When more than one type of nanoparticles are used, random and block &#8220;copolymers&#8221; of nanoparticles can be obtained. Detailed procedures are reported for the PSPAA encapsulation of nanoparticles, homo- and co-polymerization of the core-shell nanoparticles, separation and purification of the resulting nanoparticle chains. Transformations of single-line chains into double- and triple-line chains are also presented. The synergy between the polymer shell and the embedded nanoparticles leads to an unusual chain-growth polymerization mode, giving long nanoparticle chains that are distinct from the products of the traditional step-growth aggregation process.

Using Polystyrene-block-polyacrylic acid-coated Metal Nanoparticles as Monomers for Their Homo- and Co-polymerization

We report protocols for &#8220;polymerizing&#8221; various types of polymer-encapsulated metal nanoparticles into long chains of &#8220;homo-&#8220; and &#8220;co-polymers&#8221;.

We present a template-free method for &#8220;polymerizing&#8221; nanoparticles into long chains without side branches. A variety of nanoparticles are ...

Construction and Systematical Symmetric Studies of a Series of Supramolecular Clusters with Binary or Ternary Ammonium Triphenylacetates

Functions of clusters in nano or sub-nano scale significantly depend on not only kinds of their components but also arrangements, or symmetry, of their components. Therefore, the arrangements in the clusters have been precisely characterized, especially for metal complexes. Contrary to this, characterizations of molecular arrangements in supramolecular clusters composed of organic molecules are limited to a few cases. This is because construction of the supramolecular clusters, especially obtaining a series of the supramolecular clusters, is difficult due to low stability of non-covalent bonds compare to covalent bonds. From this viewpoint, utilization of organic salts is one of the most useful strategies. A series of the supramolecules could be constructed by combinations of a specific organic molecule with various counter ions. Especially, primary ammonium carboxylates are suitable as typical examples of supramolecules because various kinds of carboxylic acids and primary amines are commercially available, and it is easy to change their combinations. Previously, it was demonstrated that primary ammonium triphenylacetates using various kinds of primary amines specifically construct supramolecular clusters, which are composed of four ammoniums and four triphenylacetates assembled by charge-assisted hydrogen bonds, in crystals obtained from non-polar solvents. This study demonstrates an application of the specific construction of the supramolecular clusters as a strategy to conduct systematical symmetric study for clarification of correlations between molecular arrangements in supramolecules and kinds and numbers of their components. In the same way with binary salts composed of triphenylacetates and one kind of primary ammoniums, ternary organic salts composed of triphenylacetates and two kinds of ammoniums construct the supramolecular clusters, affording a series of the supramolecular clusters with various kinds and numbers of the components.

This article describes construction of a series of hydrogen-bonding supramolecular clusters in crystals using primary ammonium triphenylacetates, which are recrystallized from non-polar solvents. This selective construction of the supramolecular clusters leads to effective systematical symmetric studies about a correlation between the supramolecular clusters and their components.

Functions of clusters in nano or sub-nano scale significantly depend on not only kinds of their components but also arrangements, or symmetry, of their ...

Controlled Synthesis and Fluorescence Tracking of Highly Uniform Poly(N-isopropylacrylamide) Microgels

Stimuli-sensitive poly(N-isopropylacrylamide) (PNIPAM) microgels have various prospective practical applications and uses in fundamental research. In this work, we use single particle tracking of fluorescently labeled PNIPAM microgels as a showcase for tuning microgel size by a rapid non-stirred precipitation polymerization procedure. This approach is well suited for prototyping new reaction compositions and conditions or for applications that do not require large amounts of product. Microgel synthesis, particle size and structure determination by dynamic and static light scattering are detailed in the protocol. It is shown that the addition of functional comonomers can have a large influence on the particle nucleation and structure. Single particle tracking by wide-field fluorescence microscopy allows for an investigation of the diffusion of labeled tracer microgels in a concentrated matrix of non-labeled microgels, a system not easily investigated by other methods such as dynamic light scattering.

Controlled Synthesis and Fluorescence Tracking of Highly Uniform PolyN-isopropylacrylamide Microgels

Non-stirred precipitation polymerization provides a rapid, reproducible prototyping approach to the synthesis of stimuli-sensitive poly(N-isopropylacrylamide) microgels of narrow size distribution. In this protocol synthesis, light scattering characterization and single particle fluorescence tracking of these microgels in a wide-field microscopy setup are demonstrated.

Stimuli-sensitive poly(N-isopropylacrylamide) (PNIPAM) microgels have various prospective practical applications and uses in fundamental research. In this ...

Synthesis of Monodisperse Cylindrical Nanoparticles via Crystallization-driven Self-assembly of Biodegradable Block Copolymers

The production of monodisperse cylindrical micelles is a significant challenge in polymer chemistry. Most cylindrical constructs formed from diblock copolymers are produced by one of three techniques: thin film rehydration, solvent switching or polymerization-induced self-assembly, and produce only flexible, polydisperse cylinders. Crystallization-driven self-assembly (CDSA) is a method which can produce cylinders with these properties, by stabilizing structures of a lower curvature due to the formation of a crystalline core. However, the living polymerization techniques by which most core-forming blocks are formed are not trivial processes and the CDSA process may yield unsatisfactory results if carried out incorrectly. Here, the synthesis of cylindrical nanoparticles from simple reagents is shown. The drying and purification of reagents prior to a ring-opening polymerization of &#949;-caprolactone catalyzed by diphenyl phosphate is described. This polymer is then chain extended by methyl methacrylate (MMA) followed by N,N-dimethyl acrylamide (DMA) using reversible addition&#8722;fragmentation chain-transfer (RAFT) polymerization, affording a triblock copolymer that can undergo CDSA in ethanol. The living CDSA process is outlined, the results of which yield cylindrical nanoparticles up to 500 nm in length and a length dispersity as low as 1.05. It is anticipated that these protocols will allow others to produce cylindrical nanostructures and elevate the field of CDSA in the future.

Crystallization-driven self-assembly (CDSA) displays the unique ability to fabricate cylindrical nanostructures of narrow length distributions. The organocatalyzed ring-opening polymerization of &#949;-caprolactone and subsequent chain extensions of methyl methacrylate and N,N-dimethyl acrylamide are demonstrated. A living CDSA protocol that produces monodisperse cylinders up to 500 nm in length is outlined.

The production of monodisperse cylindrical micelles is a significant challenge in polymer chemistry. Most cylindrical constructs formed from diblock ...

Synthesis of Information-bearing Peptoids and their Sequence-directed Dynamic Covalent Self-assembly

This protocol presents the use of Lewis acidic multi-role reagents to circumvent kinetic trapping observed during the self-assembly of information-encoded oligomeric strands mediated by paired dynamic covalent interactions in a manner mimicking the thermal cycling commonly employed for the self-assembly of complementary nucleic acid sequences. Primary amine monomers bearing aldehyde and amine pendant moieties are functionalized with orthogonal protecting groups for use as dynamic covalent reactant pairs. Using a modified automated peptide synthesizer, the primary amine monomers are encoded into oligo(peptoid) strands through solid-phase submonomer synthesis. Upon purification by high-performance liquid chromatography (HPLC) and characterization by electrospray ionization mass spectrometry (ESI-MS), sequence-specific oligomers are subjected to high-loading of a Lewis acidic rare-earth metal triflate which both deprotects the aldehyde moieties and affects the reactant pair equilibrium such that strands completely dissociate. Subsequently, a fraction of the Lewis acid is extracted, enabling annealing of complementary sequence-specific strands to form information-encoded molecular ladders characterized by matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS). The simple procedure outlined in this report circumvents kinetic traps commonly experienced in the field of dynamic covalent assembly and serves as a platform for the future design of robust, complex architectures.

A protocol is presented for the synthesis of information-encoded peptoid oligomers and for the sequence-directed self-assembly of these peptoids into molecular ladders using amines and aldehydes as dynamic covalent reactant pairs and Lewis acidic rare-earth metal triflates as multi-role reagents.

This protocol presents the use of Lewis acidic multi-role reagents to circumvent kinetic trapping observed during the self-assembly of information-encoded ...

Self-Assembly of Polymer-Grafted Metal Organic Framework Monolayers

Synthesis and Characterization of Self-Assembled Metal-Organic Framework Monolayers Using Polymer-Coated Particles

Metal-organic frameworks (MOFs) are materials with potential applications in fields such as gas adsorption and separation, catalysis, and biomedicine. Attempts to enhance the utility of MOFs have involved the preparation of various composites, including polymer-grafted MOFs. By directly grafting polymers to the external surface of MOFs, issues of incompatibility between polymers and MOFs can be overcome. Polymer brushes grafted from the surface of MOFs can serve to stabilize the MOF while enabling particle assembly into self-assembled metal-organic framework monolayers (SAMMs) via polymer-polymer interactions.
Control over the chemical composition and molecular weight of the grafted polymer can allow for tuning of the SAMM characteristics. In this work, instructions are provided on how to immobilize a chain transfer agent (CTA) onto the surface of the MOF UiO-66 (UiO = Universitetet i Oslo). The CTA&#160;serves as initiation sites for the growth of polymers. Once polymer chains are grown from the MOF surface, the formation of SAMMs is achieved through self-assembly at an air-water interface. The resulting SAMMs are characterized and shown to be freestanding by scanning electron microscopy imaging. The methods presented in this paper are expected to make the preparation of SAMMs more accessible to the research community and thereby expand their potential use as a&#160;MOF-polymer composite.

Author Spotlight: Exploring Self-Assembled MOF-Polymer Composites

A protocol for the synthesis and characterization of self-assembled metal-organic framework monolayers is provided using polymer-grafted, metal-organic framework (MOF) crystals. The procedure shows that polymer-grafted MOF particles can be self-assembled at an air-water interface resulting in well-formed, free-standing, monolayer structures as evidenced by scanning electron microscopy imaging.

Metal-organic frameworks (MOFs) are materials with potential applications in fields such as gas adsorption and separation, catalysis, and biomedicine. ...

Characterization of pH-Dependent Reversible Self-Assembly of Amyloid Beta 1-40-Coated Gold Colloids

The characterization of A&#946;1-40 coated over the nano-gold colloidal particle surfaces was conducted using surface plasmon resonance (SPR) spectroscopy and transmission electron microscopy (TEM). The observed pH-dependent shift of the SPR band of A&#946;1-40-coated 20 nm gold particles was correlated with alternation of aggregation and disaggregation observed in the TEM images. A pH of ~4&#160;induced an unfolded conformation, and a pH of ~10&#160;induced a folded conformation of A&#946;1-40 on the gold surface. This reversible aggregation process was observed by Raman imaging as the pH was gradually changed from pH 4 to pH 10. We observed a pH-dependent morphology change in A&#946;1-40 on the gold surface, where clear aggregates were observed at pH 4. However, we observed very subtle differences in the surface-enhanced Raman spectroscopy (SERS) spectrum between pH 4 and pH 10 conditions, with the most striking difference being spectral density in the region of 250 cm-1 and 1750 cm-1. Specifically, the mode analysis of the reversible aggregation indicated that the aggregates were formed by the unfolded conformation of A&#946;1-40 which involved the benzene ring section of Tyrosine and Phenylalanine. Conversely, the disassembly of the aggregates was associated with conformational changes in protein folding of A&#946;1-40 involving Histidine, Glutamine, Methionine, and Aspartic acid.

Here, we present a systematic method describing the quasi-reversible self-assembly of the amyloid beta 1-40 (A&#946;1-40)-coated 20 nm gold aggregates. The nano-size-dependent quasi-reversible networking between peptides was correlated with specific amino acids or sections of the A&#946;1-40 monomer.

The characterization of A&#946;1-40 coated over the nano-gold colloidal particle surfaces was conducted using surface plasmon resonance (SPR) spectroscopy ...

Biochemistry

Colloids

Children at play often make suspensions such as mixtures of mud and water, flour and water, or a suspension of solid pigments in water known as tempera paint. These suspensions are heterogeneous mixtures composed of relatively large particles that are visible to the naked eye or can be seen with a magnifying glass. They are cloudy, and the suspended particles settle out after mixing. On the other hand, a solution is a homogeneous mixture in which no settling occurs and in which the dissolved species are molecules or ions. Solutions exhibit completely different behavior from suspensions. A solution may be colored, but it is transparent, the molecules or ions are invisible, and they do not settle out on standing. Another class of mixtures called colloids (or colloidal dispersions) exhibit properties intermediate between those of suspensions and solutions. The particles in a colloid are larger than most simple molecules; however, colloidal particles are small enough that they do not settle out upon standing.
Preparation of Colloidal Systems
Colloids are prepared by producing particles of colloidal dimensions and distributing these particles throughout a dispersion medium. Particles of colloidal size are formed by two methods: 
 
&#8226; Dispersion methods: breaking down larger particles. For example, paint pigments are produced by dispersing large particles by grinding in special mills. 
&#8226;&#160;Condensation methods: growth from smaller units, such as molecules or ions. For example, clouds form when water molecules condense and form very small droplets.
A few solid substances, when brought into contact with water, disperse spontaneously and form colloidal systems. Gelatin, glue, starch, and dehydrated milk powder behave in this manner. The particles are already of colloidal size; the water simply disperses them. Powdered milk particles of colloidal size are produced by dehydrating milk spray. Some atomizers produce colloidal dispersions of a liquid in air.
An emulsion may be prepared by shaking together or blending two immiscible liquids. This breaks one liquid into droplets of colloidal size, which then disperse throughout the other liquid. Oil spills in the ocean may be difficult to clean up, partly because wave action can cause the oil and water to form an emulsion. In many emulsions, however, the dispersed phase tends to coalesce, form large drops, and separate. Therefore, emulsions are usually stabilized by an emulsifying agent, a substance that inhibits the coalescence of the dispersed liquid. For example, a little soap will stabilize an emulsion of kerosene in water. Milk is an emulsion of butterfat in water, with the protein casein serving as the emulsifying agent. Mayonnaise is an emulsion of oil in vinegar, with egg yolk components as the emulsifying agents.
Condensation methods form colloidal particles by aggregation of molecules or ions. If the particles grow beyond the colloidal size range, drops or precipitates form, and no colloidal system results. Clouds form when water molecules aggregate and form colloid-sized particles. If these water particles coalesce to form adequately large water drops of liquid water or crystals of solid water, they settle from the sky as rain, sleet, or snow. Many condensation methods involve chemical reactions. A red colloidal suspension of iron(III) hydroxide may be prepared by mixing a concentrated solution of iron(III) chloride with hot water:
&#160;<img alt="Eq1" src="/files/ftp_upload/11372/11372_Equation 1.png" style="height: 50px;" />
A colloidal gold sol results from the reduction of a very dilute solution of gold(III) chloride by a reducing agent such as formaldehyde, tin(II) chloride, or iron(II) sulfate:
&#160;<img alt="Eq2" src="/files/ftp_upload/11372/11372_Equation 2v2.png" style="height: 50px;" />
Some gold sols prepared in 1857 are still intact (the particles have not coalesced and settled), illustrating the long-term stability of many colloids.
Soaps and Detergents
Pioneers made soap by boiling fats with a strongly basic solution made by leaching potassium carbonate, K2CO3, from wood ashes with hot water. Animal fats contain polyesters of fatty acids (long-chain carboxylic acids). When animal fats are treated with a base like potassium carbonate or sodium hydroxide, glycerol and salts of fatty acids such as palmitic, oleic, and stearic acid are formed. The salts of fatty acids are called soaps. The sodium salt of stearic acid, sodium stearate, contains an uncharged nonpolar hydrocarbon chain, the C17H35 unit, and an ionic carboxylate group, the COO&#8722; unit.
The cleaning action of soaps and detergents can be explained in terms of the structures of the molecules involved. The hydrocarbon (nonpolar) end of a soap or detergent molecule dissolves in or is attracted to nonpolar substances, such as oil, grease, or dirt particles. The ionic end is attracted by water (polar). As a result, the soap or detergent molecules become oriented at the interface between the dirt particles and the water, so they act as a kind of bridge between two different kinds of matter, nonpolar and polar. Molecules such as this are termed amphiphilic since they have both a hydrophobic (&#8220;water-fearing&#8221;) part and a hydrophilic (&#8220;water-loving&#8221;) part. As a consequence, dirt particles become suspended as colloidal particles and are readily washed away.
This text is adapted from <a href="https://openstax.org/books/chemistry-2e/pages/11-5-colloids">Openstax, Chemistry 2e, Section 11.5: Colloids.</a>

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