Article pubs.acs.org/Langmuir
Domed Silica Microcylinders Coated with Oleophilic Polypeptides and Their Behavior in Lyotropic Cholesteric Liquid Crystals of the Same Polypeptide Cornelia Rosu,*,†,⊥ Shane Jacobeen,‡ Katherine Park,# Elsa Reichmanis,*,†,§,∥,⊥ Peter Yunker,‡ and Paul S. Russo*,†,∥,⊥ †
School of Materials Science of Engineering, ‡School of Physics, §School of Chemical and Biomolecular Engineering, ∥School of Chemistry and Biochemistry, and ⊥GTPN-Georgia Tech Polymer Network, Georgia Institute of Technology, Atlanta, Georgia 30332, United States # Molecular Vista, Inc., 6840 Via Del Oro, Suite 110, San Jose, California 95119, United States S Supporting Information *
ABSTRACT: Liquid crystals can organize dispersed particles into useful and exotic structures. In the case of lyotropic cholesteric polypeptide liquid crystals, polypeptide-coated particles are appealing because the surface chemistry matches that of the polymeric mesogen, which permits a tighter focus on factors such as extended particle shape. The colloidal particles developed here consist of a magnetic and fluorescent cylindrically symmetric silica core with one rounded, almost hemispherical end. Functionalized with helical poly(γ-stearyl-Lglutamate) (PSLG), the particles were dispersed at different concentrations in cholesteric liquid crystals (ChLC) of the same polymer in tetrahydrofuran (THF). Defects introduced by the particles to the director field of the bulk PSLG/THF host led to a variety of phases. In fresh mixtures, the cholesteric mesophase of the PSLG matrix was distorted, as reflected in the absence of the characteristic fingerprint pattern. Over time, the fingerprint pattern returned, more quickly when the concentration of the PSLG-coated particles was low. At low particle concentration the particles were “guided” by the PSLG liquid crystal to organize into patterns similar to that of the re-formed bulk chiral nematic phase. When their concentration increased, the well-dispersed PSLG-coated particles seemed to map onto the distortions in the bulk host’s local director field. The particles located near the glass vial−ChLC interfaces were stacked lengthwise into architectures with apparent two-dimensional hexagonal symmetry. The size of these “crystalline” structures increased with particle concentration. They displayed remarkable stability toward an external magnetic field; hydrophobic interactions between the PSLG polymers in the shell and those in the bulk LC matrix may be responsible. The results show that bio-inspired LCs can assemble suitable colloidal particles into soft crystalline structures.
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INTRODUCTION Colloid-containing cholesteric liquid crystals (CChLCs) are an emergent and appealing class of soft matter because of their remarkable biological and optical properties.1−3 Like their nematic counterparts, CChLCs combine colloidal assembly with the ability of the bulk ChLC host to respond to external stimuli (e.g., electric and magnetic fields, ionic strength, temperature).4−7 Particles deform the local liquid crystal director, creating new director fields and topological defects.8,9 In response, the counteractive elastic forces of the liquid crystal host drive the system to new equilibrium states. Many times this behavior facilitates assembly of particles into 2D and 3D arrays.10,11 Most works that investigate CChLCs12,13 use cholesteric matrices formed by nematic liquid crystals with chiral dopants.14 Although most studies have been conducted with common nematic mesogens, polymeric liquid crystal hosts deserve attention,15 especially biopolymers16 because of their © 2016 American Chemical Society
ability to form cholesteric phases. These twisted nematic phases add richness to the complex fluids behavior due to the subtle yet profound effects of molecular chirality.17 Few works harness the ability of biopolymers to order into nematic twisted phases16 despite the fact that some, such as deoxyribonucleic acid (DNA), form cholesteric liquid crystals,18,19 even in living organisms.20,21 Even less explored is the capability of these polymers to induce order in other functional materials, especially in colloidal-based systems. DNA was used as “glue” that facilitated particle assembly into supramolecular and programmable structures.22−24 While the phase behavior of DNA-derived systems has been studied,24−26 less is known about DNA-based CChLCs.26 For example, gold multifuncReceived: August 25, 2016 Revised: November 16, 2016 Published: November 30, 2016 13137
DOI: 10.1021/acs.langmuir.6b03165 Langmuir 2016, 32, 13137−13148
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(28−30%) ACS grade was purchased from BDH Aristar. All reagents were used without further purification. Deionized water (18 MΩ·cm) was drawn from a Barnstead Nanopure water purification system. Detailed Synthetic Procedures. Preparation of Silica, HemiSil. The preparation of the anisotropic silica followed the Kuijk et al. procedure.49 Yield of nearly monodisperse HemiSil: 600 mg. Preparation of Magnetic Silica, MHemiSil. Magnetic silica particles were synthesized using a modified Kuijk et al. procedure.49 Typically, in a 500 mL capped glass bottle, PVP (30 g, Mn = 40 000 g mol−1) was dissolved in 300 mL of 1-pentanol by sonication at room temperature until the mixture became clear. Magnetite particles (D = 11 ± 1 nm, 100 mg dispersed in 4 mL of 1-pentanol)50 were probe sonicated separately for 20 min and then introduced to the PVP/1-pentanol mixture. The magnetic mixture was shaken vigorously by hand (15 min) and sonicated for another 20 min. Absolute EtOH (30 mL), pure water (8.4 mL), and sodium citrate dihydrate (2 mL of 0.18 M aqueous solution) were added, and the bottle was shaken again by hand (15 min) to mix the content. Then, ammonium hydroxide (6.75 mL) was fed into the bottle which was shaken again for 15 min. The last reagent introduced to the reaction mixture was TEOS (3 mL), and vigorous manual shaking was applied for another 15 min. Finally, the mixture was allowed to rest undisturbed, while the reaction proceeded overnight (∼12−14 h). After reaction completion, the mixture was divided in 50 mL PTFE tubes and centrifuged at 1500g for 1 h. After the liquid was decanted, particles were dispersed in EtOH. The elongated silica particles were further washed following this sequence: two times with EtOH (1500g, 15 min), two times with water (1500g, 15 min), and two times with EtOH (1500g, 15 min). Smaller particles were removed from the bulk suspension by three repeat centrifugation−decantation−redispersion cycles in EtOH (700g, 10 min) to narrow the size distribution. Yield of nearly monodisperse MHemiSil particles: 650 mg. Preparation of Magnetic Fluorescent Silica, MFHemiSil. A concentrated suspension of the MHemiSil (400 mg in 10 mL of EtOH) was probe sonicated for 20 min and then diluted with 50 mL of EtOH in a round-bottom flask (250 mL). The reaction was carried out at room temperature overnight (12−14 h) with fluorescent 3aminopropyltriethoxysilane−fluorescein isothiocyanate adduct, FITCAPS (1 mL), added to the mixture. The flask was capped with a glass stopper and covered with aluminum foil to ensure darkness during overhead mechanical stirring (300 rpm). The resulting particles were washed with EtOH by centrifugation−decantation−redispersion until no fluorescence was detected in the supernatant using a 488 nm laser. They were finally dispersed in EtOH. Yield of MFHemiSil product: 420 mg. Silica Protection, SiMFHemiSil. A dispersion of MFHemiSil (300 mg in 5 mL of EtOH) was probe sonicated for 20 min and diluted with 50 mL of EtOH in a round-bottom flask (250 mL). Ammonium hydroxide (4.5 mL) was added in small portions over 5 min under overhead mechanical stirring (300 rpm) until basic pH (9) was reached. Stirring of reaction continued for another 20 min. A solution of TEOS/EtOH in a 1:4 ratio (0.5 mL TEOS:2 mL EtOH) was separately prepared and inserted into a buret connected to the reaction flask. The TEOS/EtOH solution was added dropwise at a rate of one drop per minute (∼50 μL/min). The reaction progressed overnight (12 h) at room temperature in the dark and under mechanical stirring (300 rpm). Particles were washed five times by centrifugation− decantation−redispersion in EtOH and stored in the same solvent. Yield of SiMFHemiSil product: 430 mg. Amino Functionalization of HemiSil. A concentrated suspension of HemiSil particles (300 mg, 8 mL) was probe sonicated for 20 min and diluted with EtOH (50 mL) in a round-bottom flask. A solution of methyltrimethoxysilane (MTMS) and APS in 75:25 ratio was prepared separately in 1 mL of EtOH. This solution was added to the dispersion flask while stirring (300 rpm), and the reaction proceeded overnight (12 h). The particles were washed with anhydrous EtOH until a ninhydrin test applied to the supernatant was negative. Amino Functionalization of SiMFHemiSil. This step followed the same procedure as described in the previous step. Yield of product: 280 mg per each batch.
tional nanorods acting as orientation markers and photothermal agents were able to track the reorientation of DNA strands.27 Heating the gold particles enabled control over the organization of DNA strands into lyotropic liquid crystal phases.27 Whereas DNA liquid crystal phases are aqueous,28 synthetic polypeptides are chiral, semiflexible macromolecules soluble in a variety of solvents.29−31 The stiff, rodlike structure is an attribute of the polypeptide α-helix secondary conformation that also supports the ChLC phases. The intriguing phase behavior of poly(γ-benzyl-L-glutamate) (PBLG) has made it a common model for polymer liquid crystals, especially cholesterics.29 Yet PBLG is not the only choice. Its waxy counterpart, poly(γ-stearyl-L-glutamate) (PSLG), is a hydrophobic polypeptide that forms thermotropic and lyotropic liquid crystal mesophases in a variety of organic solvents including chloroform, tetrahydrofuran, toluene, and dodecane.31−34 Relevant to this investigation is the easy attachment of PSLG to curved silica surfaces yielding composite particles.35 The properties of CChLC mixtures depend on the shape of the particle that interacts with the liquid crystal host. Most studies have used spherical particles with variable surface anchoring.12,13,36,37 Expanding the library of particles used in CChLC studies to anisotropically shaped homologues38,39 with tethered polypeptide shells would provide a convenient platform to study the effects of shape anisotropy on colloidal assembly behavior in complex fluids.40 Because the tunable shape, size, and axial ratio of uncoated anisotropic particles were observed to impact the properties of certain liquid crystal systems and colloidal crystals,15,41−47 the polypeptide composite counterparts are also expected to enrich the physical behavior of the resultant CChLCs. Just as spherical polypeptide-coated particles organize and form colloidal crystals,48 elongated polypeptide-coated particles may assemble into interesting phases of their own. Here we explore the ability of chiral polypeptides to induce ordering in CChLCs. Domed cylinders made of silica were covalently functionalized with helical PSLG. The dome on one end of the cylinder is rarely a perfect hemisphere; nevertheless, we refer to the core particles as hemispherically capped cylinders of silica, or HemiSil. The C18 side chains of PSLG are both soft and hydrophobic compared to those of most other polypeptides. In order to find the particle in the complex fluid mixtures, fluorescein dye was covalently bound into the particle core. In addition, magnetic inclusions were also incorporated to investigate the stability of the ordered colloidal structure toward applied fields. The anisotropically shaped PSLG-coated, magnetic, and fluorescent particles (PSLG-MFHemiSil) were dispersed in a PSLG/tetrahydrofuran cholesteric liquid crystal matrix, at different concentrations. The disposition of the PSLG-MFHemiSil particles within the PSLG cholesteric matrix depended on their concentration. In time, they “crystallized” and formed stable ordered assemblies of hexagonal geometry.
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MATERIALS AND METHODS
Materials. Tetraethyl orthosilicate (TEOS, 98%), L-glutamic acid (99%), stearyl alcohol (99%), tert-butanol (99.5%), anhydrous dichloromethane (DCM), anhydrous hexane, anhydrous tetrahydrofuran (THF), trimethylamine, methanol, n-butanol, 1-pentanol, polyvinylpyrollidone (PVP, Mn = 40 000 g mol−1), sodium citrate dihydrate, 3-aminopropyl)triethoxysilane (APS, 99%), methytrimethoxysilane (MTMS, 95%), fluorescein isothiocyanate (FITC, 90%) and ethyl acetate were purchased from Sigma-Aldrich. Triphosgene was obtained from TCI America. Ethyl alcohol, 200 proof ACS/USP grade, was obtained from Pharmco-AAPER. Ammonium hydroxide 13138
DOI: 10.1021/acs.langmuir.6b03165 Langmuir 2016, 32, 13137−13148
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Scheme 1. Synthetic Route for Preparation of Anisotropically Shaped Nonmagnetic and Magnetic Silica Particles Coated with Poly(γ-stearyl-L-glutamate), PSLG (PSLG-HemiSil and PSLG-SiMFHemiSil) (Not Drawn to Scale)
Preparation of γ-Stearyl-L-glutamate (SLG). The polypeptide precursor SLG was prepared following the procedure of Wasserman et al.51 Yield of SLG product: 27 g (63%). Preparation of γ-Stearyl-L-glutamate N-Carboxyanhydride (SLGNCA). The polypeptide monomer was prepared using the procedure of Daly et al.52 Yield of SLG-NCA product: 4.2 g (80%). Preparation of Poly(stearyl-L-glutamate)-Coated HemiSil by the “Grafting From” Method (PSLG-HemiSil). A flame-dried roundbottom flask (100 mL) was loaded with anhydrous DCM (40 mL) and 3 g of SLG-NCA inside a glovebag under dry nitrogen. The flask was capped with a rubber septum and swirled to dissolve the SLG-NCA solid to a clear solution. The mixture was purged for 5 min with dry nitrogen. To this mixture, amino-functionalized HemiSil particles (200 mg) suspended in 10 mL of anhydrous DCM and probe-sonicated for 5 min were injected quickly through the septum. The flask was heated to 35 °C using a heating mantle and rapidly connected to a bubbler to release the CO2 formed during reaction. The reaction proceeded under magnetic stirring. After 3 days the production of gas stopped, indicating the reaction was complete. The resulting particles were subjected to three cycles of centrifugation−decantation−redispersion with DCM followed by three cycles with THF. Yield of PSLG-HemiSil product: 210 mg. Preparation of PSLG-SiMFHemiSil. This step followed the same procedure as described in the previous step, except that SiMFHemiSil was used. Yield of PSLG-SiMFHemiSil product: 200 mg. Preparation of Colloidal Cholesteric Liquid Crystals. CChLCs were prepared in 4 mL scintillation vials sealed with PTFE-faced lids. First, a volume of 200 μL solvent and an appropriate amount of PSLG polymer (Mw = 70 000 Da) were used for a concentration of 30% (w/ w). The polymer was allowed to dissolve overnight under gentle stirring until the solution became clear. This sample was allowed to rest one more day to reach equilibrium. Vitrocom capillary cells (rectangular, 0.4 mm thick × 4 mm wide) were used to investigate the morphology of the ChLC, which was further used as a matrix for CChLCs. The Vitrocom cells were flame-sealed at both ends. To the
remaining ChLC matrix solution, volumes of particle dispersions were added to bring their concentration to 0.09, 0.18, 0.36, and 0.45 wt %. The supplemental amount of solvent introduced to the mixture was evaporated under a slow stream of dry nitrogen. Samples were equilibrated for 2 days before insertion into the same Vitrocom cells, as above-described, and investigated by polarized light microscopy. Methods. Transmission/Scanning Electron Microscopy (TEM/ SEM). Transmission/scanning electron microscopy images of particles at different stages were obtained using a JEOL 100-CX with an accelerating voltage of 80 keV and JSM-6610 (3 nm resolution depth) electron microscopes. A dilute sample solution was prepared by dispersion of 20 μL of particle suspensions in 1 mL of EtOH. The mixture was sonicated 1−2 min to ensure a good dispersion of particles. For TEM a drop was placed atop of a 400 mesh carboncoated copper grid (from Electron Microscopy Sciences). For SEM, a drop of the dispersion was placed on a small piece of mica sheet (Ted Pella Inc.) grounded to the SEM stub through a carbon conductive double-faced adhesive tape. They were sputter-coated with a layer of Pt for 4 min (1 min = 15 nm Pt deposition) before visualization. The samples were dried either ∼8 h in air or 2−3 h in vacuo. Particle size was analyzed using NIH ImageJ software. Polarized Optical Microscopy (POM). Optical images of PSLGSiMFHemiSil particles suspended in liquid crystal solutions were recorded with an Olympus polarized light optical microscope, model BH2, equipped with an AmScope color CCD camera. Thermogravimetric Analysis (TGA). TGA of samples was obtained with a TGA Q50 apparatus from TA Instruments under nitrogen flow and a heating rate of 10 °C min−1. The mass of the specimen was in the range of 3−10 mg. Photoinduced Force Microscopy (PiFM). An atomic force microscope (VistaScope) from Molecular Vista was used for the AFM and PiFM measurements. The microscope was operated in noncontact (tapping) mode in air with a gold-coated cantilever (PPP-NCHAu) from Nanosensors. The tunable IR excitation laser used for the PiFM measurements was a LaserTune from Block Engineering, with ∼1 mW 13139
DOI: 10.1021/acs.langmuir.6b03165 Langmuir 2016, 32, 13137−13148
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Langmuir of laser power at the sample. A 3 μm × 3 μm AFM topography image was taken by locating two particles from the sample in the dried state. The first PiFM spectrum was taken on the silicon wafer substrate (off) and on particle surface from 1500 to 1700 cm−1 with an exposure time of 100 ms per wavenumber. Another AFM topography image (500 nm × 500 nm) was then taken by zooming in on the particles. Six PiFM spectra, each from 1500 to 1700 cm−1, were recorded at different locations atop the particles to compare with the same number of spectra taken on the substrate. PiFM images were acquired simultaneously with the AFM topography images while the tunable IR excitation laser was fixed at 1660 cm−1 (amide I of helical PSLG). Confocal Scanning Laser Microscopy. Three-dimensional images were obtained using a Nikon A1R confocal microscope. Excitation of the sample was achieved by a 488 nm laser.
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RESULTS AND DISCUSSION Design of Responsive Dome-Capped Cylindrical Silica Composite Particles. The preparation of anisotropicallyTable 1. Sample Code and Sizes Measured by Scanning Electron Microscopy TEM sample code
L/nm
D/nm
L/D
HemiSil MHemiSil SiMFHemiSil
1440 ± 98 2380 ± 180 2570 ± 250
560 ± 83 510 ± 71 610 ± 60
2.6 ± 0.22 4.6 ± 0.43 4.2 ± 0.01
Figure 2. Photoinduced force microscopy (PiFM) typical results: (A, B) PiFM images overlaid on 3D topography images show distribution of the PSLG polypeptide (the orange regions identify where the PSLG polypeptide is located). The black points represent the locations on the PSLG-HemiSil surface where PiFM spectra were collected, while the red point indicates the off particle location used to collect a PiFM spectrum. (C) PiFM signal versus wavenumber for the locations indicated by the black and red dots, showing the amide I and amide II signals characteristic of the PSLG polypeptide. Exposure time was 100 ms per wavenumber.
shaped nonmagnetic silica, HemiSil, followed the one-pot method reported by Kuijk et al.,49 as illustrated in Scheme 1, part I (step A). After preparation, the surface of HemiSil was functionalized with amino groups by using an activator− passivator pair, APS-MTMS, in a ratio of 1:3. MTMS acts as a spacer between the amino functional groups and benefits the growth of the polypeptide chains from the surface. The growing f rom method was used to functionalize HemiSil cores with the PSLG shell.50 In this method, the ring-opening polymerization of SLG-NCA, the polypeptide precursor, initiated by the
amino-primed cores enables the growth of the polypeptide shell from the particle surface (Scheme 1A). In order to make the PSLG−silica composite particle responsive, magnetite particles were introduced to the emulsion mixture during the first step (Scheme 1B) to produce the
Figure 1. Scanning electron micrographs of (A) silica, HemiSil; (B) magnetic silica, MHemiSil; and (C) protected magnetic fluorescent magnetic silica, SiMFHemiSil. Transmission electron microscopy images of (D) HemiSil showing the appearance of the two different ends, (E) magnetite particles situated within the round end of MHemiSil, and (F) the appearance of the MFHemiSil particle surface. 13140
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Figure 3. Thermogravimetric curves showing the percentage of mass loss for particles after each step of PSLG-HemiSil and PSLG-SiMFHemiSil preparation (A). The corresponding weight derivatives showing the decomposition peak positions matching for untethered PSLG, PSLGSiMFHemiSil, PSLG-HemiSil, and HemiSil (B).
Figure 4. Appearance of colloidal cholesteric liquid crystal, CChLC, PSLG-SiMFHemiSil/PSLG-70000/THF, after 1 week: Optical micrographs (A1 and B1), polarized optical micrographs (A2 and B2), and epifluorescence images showing the presence of particles at the PSLG ChLC−glass vial interface (A3 and B3). Images A2 and B2 were visualized under crossed polarizers set at 90° and using a color plate.
anisotropic magnetic silica cores (MHemiSil, Scheme 1, part II). Fluorescence was realized by covalent attachment of the FITC-APS adduct.53 The surface of the MFHemiSil was protected with an additional silica layer to prevent the dye from leaking and bleaching (SiMFHemiSil). Next, the PSLG shell was grown from the SiMFHemiSil surface following the same steps as described for nonmagnetic composites and yielded PSLG-SiMFHemiSil particles (Scheme 1, part II). Characterization of Responsive Dome-Capped Cylindrical Silica Composite Particles. The shape and size of the silica particles, summarized in Table 1, were evaluated by SEM and TEM. Nonmagnetic HemiSil particles, shown in Figures 1A and 1D, took the shape of a domed cylinder: one round and one flat end. The lighter appearance at the particle edges when compared to its center (Figure 1D) is evidence that it is not a flat surface. Addition of magnetite particles to the reaction mixture yielded anisotropic silica with a higher aspect ratio, as seen in Figure 1B. The SEM image of MHemiSil reveals an interesting feature: the round tip has a mushroom-like shape and appears brighter. TEM analysis showed that this architecture is due to magnetite particle agglomerates that positioned themselves
only within the rounded end (Figure 1E). Incorporation of both the dye adduct FITC-APS and TEOS layer led to the formation of magnetic fluorescent silica, MFHemiSil; its surface was coated with an additional silica layer (Figure 1C). The silica protective shell did not uniformly cover the MFHemiSil surface, most probably due to its roughness. Surface irregularities can act as nucleation points for silica growth.54 The axial ratio of the resulting SiMFHemiSil was slightly smaller than that of MFHemiSil, 4.2 vs 4.6, but their thickness was larger. The L/D value does not take into account the little silica spheres deposited at the particle surface. Typically in the regrowth process, silica grows uniformly at the surface of the seeds, improving their size distribution. Because the surface of the MFHemiSil had irregularities, as shown in Figure 1F, most of the TEOS was probably consumed in the growth of silica spheres generated by secondary nucleation at the surface of the parent anisotropic core. Regardless of their compositions and response, a common feature observed in SEM images was the tendency of the particles to align and arrange into ordered domains upon drying on solid substrates. Normally, TEM and SEM measurements on particles are backed up by dynamic light scattering (DLS) to guard against 13141
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Figure 5. Time evolution of 0.09 wt % PSLG-SiMFHemiSil/30 wt % PSLG-70000/THF: Optical micrographs recorded by in-depth focusing after 2 weeks (A1 and B1) and after 1 month (B1 and B2). The A2 and B2 images were recorded using an analyzer and polarizer crossed at 90°. A color plate was inserted. The white arrows in A1 and B1 point to particles seen to follow the disclinations within the PSLG ChLC. The sample in B1 and B2 was exposed to an external magnetic field provided by a neodymium permanent magnet, (B = 0.425 mT) for 2 weeks. In (A2) and (B2) the white lines and numbers correspond to the half-pitch, p/2 values.
polypeptide chains growing from the surface is short and does not allow folding into a helical conformation.29 Thermogravimetric analysis (Figure 3) provided additional confirmation of the presence of PSLG polypeptide on the surfaces of the silica particles. The decomposition events seen in the TGA traces (Figure 3A) up to 200 °C are due to absorbed and H-bonded water. This temperature also marks thermal degradation of the long stearyl aliphatic side chains anchored to the PSLG backbone. The main PSLG chain decomposes between 300 and 600 °C. Comparison between the TGA profiles of pure silica, HemiSil, and PSLG-functionalized cores reveals a PSLG mass percent loading of about 10% for both magnetic (PSLG-SiMFHemiSil) and nonmagnetic (PSLG-HemiSil) analogues. This percentage accounts for a relatively small polypeptide payload on the particle surface. The presence of the PSLG polypeptide shell grafted from the silica cores was also evident from the mass derivative curves (Figure 3B). The endothermic peak associated with the decomposition of polypeptide is centered at ∼350 °C while pure silica gives signals between 400 and 600 °C. The position of the peaks associated with the decomposition of the PSLG backbone in the 290−300 °C temperature regions for PSLG-coated particles is close to that of untethered PSLG polymer and confirms the presence of the polypeptide on the particle surface. The shift to slightly lower temperature can be due to tethering effects. Behavior of Magnetic and Fluorescent PSLG-Coated Dome-Capped Cylindrical Silica in PSLG Cholesteric Liquid Crystals. The PSLG-coated, magnetic, and fluorescent silica composite particles, PSLG-SiMFHemiSil, were dispersed in a PSLG/THF cholesteric liquid crystal matrix to study the nature of the interactions in the PSLG-based colloidal
under sampling. Agreement between the DLS and TEM or SEM sizes also speaks to the state of aggregation of the particles in suspension. Despite complications arising from their very large size, multiangle DLS correlation functions of good quality were obtained on the hemicylindrical silica dispersed in EtOH (not shown), but the analysis of large, cylindrically symmetric objects is complicated by rotational diffusion (estimated to be
