Phospholipid-assisted synthesis of stable F-containing colloidal particles and their film formation

This letter illustrates for the first time the preparation of p-methyl methacrylate/n-butyl acrylate/heptadecafluorodecyl methacrylate (p-MMA/nBA/FMA) colloidal dispersions containing up to 15% w/w FMA, which is accomplished by the utilization of biologically active phospholipids (PLs) and ionic surfactants. The use of monomer-starved conditions during emulsion polymerization and the utilization of 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), sodium dodecyl sulfate (SDS), and phosphoric acid bis(tridecafluoro-octyl) ester ammonium salt (FSP) as surfactants, which function as transfer and dispersing agents, facilitate a suitable environment for the polymerization of p-MMA/nBA/FMA colloidal dispersions that exhibit nonspherical particle morphologies. Such nonspherical particles upon coalescence form phase-separated films with unique surface properties.     

Molecular recognition at methyl methacrylate/n-butyl acrylate (MMA/nBA) monomer unit boundaries of phospholipids at p-MMA/nBA copolymer surfaces

Lipid structural features and their interactions with proteins provide a useful vehicle for further advances in membrane proteins research. To mimic one of potential lipid-protein interactions we synthesized poly(methyl methacrylate/ n-butyl acrylate) (p-MMA/nBA) colloidal particles that were stabilized by phospholipid (PLs). Upon the particle coalescence, PL stratification resulted in the formation of surface localized ionic clusters (SLICs). These entities are capable of recognizing MMA/nBA monomer interfaces along the p-MMA/nBA copolymer backbone and form crystalline SLICs at the monomer interface. By utilizing attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectroscopy and selected area electron diffraction (SAD) combined with ab initio calculations, studies were conducted that identified the origin of SLICs as well as their structural features formed on the surface of p-MMA/nBA copolymer films stabilized by 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) PL. Specific entities responsible for SLIC formation are selective noncovalent bonds of anionic phosphate and cationic quaternary ammonium segments of DLPC that interact with two neighboring carbonyl groups of nBA and MMA monomers of the p-MMA/nBA polymer backbone. To the best of our knowledge this is the first example of molecular recognition facilitated by coalescence of copolymer colloidal particles and the ability of PLs to form SLICs at the boundaries of the neighboring MMA and nBA monomer units of the p-MMA/nBA chain. The dominating noncovalent bonds responsible for the molecular recognition is a combination of H-bonding and electrostatic interactions.     

Stimuli-responsive surface localized ionic cluster (SLICs) formation from nonspherical colloidal particles

Structural features of phospholipids provide a unique opportunity for utilizing these amphiphilic species to stabilize the synthesis of colloidal dispersion particles by controlling concentration levels relative to dispersion synthesis components. 1,2-Bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DCPC) phospholipid was utilized as cosurfactant in the synthesis of sodium dioctyl sulfosuccinate (SDOSS) stabilized methyl methacrylate/n-butyl acrylate (MMA/nBA) colloidal dispersions. Aqueous dispersions containing various concentration levels of DCPC result in the formation of cocklebur particle morphologies, and when prepared in the presence of Ca2+ and annealed at various temperatures, stimuli-responsive behaviors of coalesced films were elucidated. The formation of surface localized ionic clusters (SLICs) at the film-air (F-A) and film-substrate (F-S) interfaces is shown to be responsive to concentration levels of DCPC, Ca2+/DCPC ratios, and temperature. These studies show that it is possible to control stratification and mobility to the F-A and F-S interfaces during and after coalescence. Using attenuated total reflectance Fourier transform infrared (ATR-FTIR) and internal reflection infrared imaging (IRIRI) spectroscopies, molecular entities responsible for SLIC formation were determined. These studies also show that stimuli-responsive behaviors during film formation can be controlled by colloidal solution morphologies and synergistic interactions of individual components.     

Stimuli-responsive surface crystallization of phospholipids from bimodal colloidal particles

These studies focus on the effect of phospholipids in the presence of ionic surfactants on the behavior of poly(methylmethactrylate/n-butyl acrylate) (p-MMA/nBA) colloidal particles during film formation. With the presence of two surfactants, it is possible to obtain particles that exhibit two distinct particle sizes. The presence of hydrogenated soybean phosphatidylcholine (HSPC) and sodium dioctyl sulfosuccinate (SDOSS), which stabilize these bimodal colloidal dispersions, has a significant effect on the mobility of individual components during coalescence. Specifically, the presence of HSPC inhibits migration of SDOSS to the film-air (F-A) interface. Furthermore, the presence of electrolyte species such as aqueous CaCl2 has a very pronounced effect on film formation. When the Ca2+/HSPC ratio is 0.1/1.0, SDOSS is released to the F-A interface during coalescence. At 2.0/1.0 Ca2+/HSPC, HSPC diffuses to the F-A interface and crystalline domains consisting of HSPC are formed. This stimuli-responsive behavior is confirmed using IRIR imaging that ultimately exhibits different surface morphologies. These studies illustrate for the first time that it is possible to control the release of two different surface-active species during coalescence that form crystalline domains.     

Release and formation of surface-localized ionic clusters (SLICs) into phospholipid rafts from colloidal solutions during coalescence

Stimuli-responsive behavior of phospholipids in the presence of ionic surfactants utilized in synthesis of MMA/nBA colloidal particles was investigated. Utilizing 1-myristoyl-2-hydroxy-sn-glycero-phosphocholine (MHPC) phospholipid, and sodium dioctyl sulfosuccinate (SDOSS) surfactant as dispersing media in H(2)O, narrow unimodal particle size distributions of methyl methacrylate (MMA)/n-butyl acrylate (nBA) copolymers were synthesized. The particle diameters were 154 nm when a SDOSS/MHPC mixture was used and 161 nm using MHPC as the only surface-stabilizing species. When such colloidal dispersions are exposed to 1.7, 3.3, and 6.7 mM aqueous CaCl(2) and KCl electrolyte solutions, surface-localized ionic clusters are generated at the film-air interface that may serve as lipid rafts composed of crystalline phases of MHPC deposited on poly(MMA)/nBA films. These studies illustrate that it is possible to control release and morphology developments of surface phospholipid rafts on artificial surfaces.     

Surface self-assembly of fluorosurfactants during film formation of MMA/nBA colloidal dispersions

These studies focus on the behavior of fluorosurfactants (FS) containing hydrophobic and ionic entities in the presence of methyl methacrylate/n-butyl acrylate (MMA/nBA) colloidal dispersions stabilized by sodium dodecyl sulfate (SDS). The presence of FS significantly not only alters the mobility of SDS in MMA/nBA films, but their hydrophobic and ionic nature results in self-assembly near the film-air (F-A) interface leading to different surface morphologies. Spherical islands and rodlike morphologies are formed which diminish the kinetic coefficient of friction of films by at least 3 orders of magnitude, and the presence of dual hydrophobic tails and an anionic head appears to have the largest effect on the surface friction. Using internal reflection IR imaging, these studies show that structural and chemical features of FS are directly related to their ability to migrate to the F-A interface and self-assemble to form specific morphological features. While the anionic nature of FS allows for SDS migration to the F-A interface and the formation of stable domains across the surface, intermolecular cohesion of nonionic FS allows for the formation of rodlike structures due to inability to form mixed micelles with SDS. These studies also establish the relationship between surface morphologies, kinetic coefficient of friction, and structural features of surfactants in the complex environments.     

Phase behavior of binary blends of diblock copolymer/homopolymer confined in spherical nanopores

Binary blends of a diblock copolymer (AB) and an incompatible homopolymer (C) confined in spherical cavities are studied using a simulated annealing technique. The phase behavior of the blends is examined for four typical cases, representing the different selectivity of the pore surface to the A, B, and C species. The internal morphology of the spherical polymeric particles is controlled by the homopolymer volume fraction, the degree of confinement, and the composition of the copolymer. Inside a particle, the homopolymers segregate to form one or, under some conditions, two domains; thus, the homopolymers may act as an additional controlling parameter of the shape and symmetry of the copolymer domain. A rich array of confinement-induced novel diblock copolymer morphologies is predicted. In particular, core-shell particles with the copolymers as the shell wrapping around a homopolymer core or a copolymer-homopolymer combined core and Janus-like particles with the copolymers and the homopolymers on different sides are obtained.     

Self-stratified films obtained from poly(methyl methacrylate/n-butyl acrylate) colloidal dispersions containing poly(vinyl alcohol): a spectroscopic study

These studies focus on the role of poly(vinyl alcohol) (pVOH) during colloidal synthesis of poly(methyl methacrylate/n-butyl acrylate) (pMMA/nBA) and its effect on particle coalescence. Using 2D photoacoustic FT-IR spectroscopy and internal reflection IR imaging, we showed that the presence of pVOH creates competing environments between the copolymer particle surfaces, aqueous phases, and dispersing agents which results in migration and self-induced stratification occurring during coalescence. pMMA/nBA/pVOH films stratify to form sodium dodecyl sulfate rich film-air interfaces, and the -SO3- moieties exhibit preferential parallel orientation with respect to the surface. At the same time, the bulk of the film is dominated by intramolecular hydrogen bonding between the pVOH phase and the copolymer matrix. This behavior is attributed to significant interactions between pVOH and pMMA/nBA, resulting in limited mobility of pVOH.     

Cocklebur-shaped colloidal dispersions

Unique cocklebur-shaped colloidal dispersions were prepared using a combination of a nanoextruder applied to the aqueous solution containing methyl methacrylate (MMA) and n-butyl acrylate (n-BA) with azo-bis-isobutyronitrile (AIBN) or potassium persulfate (KPS) initiators and stabilized by a mixture of sodium dioctyl sulfosuccinate (SDOSS) and 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DCPC) phospholipid. Upon extrusion and heating to 75 degrees C, methyl methacrylate/n-butyl acrylate (MMA/nBA) colloidal particles containing tubules pointing outward were obtained as a result of DCPC phospholipids present at the particle surfaces. The same cocklebur-shaped particles were obtained when classical polymerization was used without a nanoextruder under similar compositional and thermal conditions, giving a particle size of 159 nm. However, when Ca(2+) ions are present during polymerization, cocklebur morphologies are disrupted. Because DCPC tubules undergo a transition at 38 degrees C, such cocklebur morphologies may offer numerous opportunities for devices with stimuli-responsive characteristics.     

Structural morphology of poly(styrene)-poly(butyl acrylate) polymer-polymer composites studied by dynamic mechanical measurements

The emulsion polymerization process allows production of polymer particles with different structural morphologies. Films obtained after coalescence keep some memory of this morphology, but large modifications can occur during coalescence. In the present case, one of the polymers, polystyrene (PS), exhibits a glass temperature (Tg) much higher than the filmification temperature (close to room temperature), while the other one, poly(butyl acrylate) (PBA), has a much lowerTg. Furthermore, it is well known that dynamic mechanical measurements can be very helpful in providing information on the morphology of polymer materials, i.e., on geometrical and topological arrangement of homopolymer domains. At first, this method was used for comparison of two types of films: i) the first one obtained from structured-core (PS)-shell (PBA) particles, ii) the second one obtained from a blend of homopolymer particles (PS and PBA). It appears that the expected core-shell particles lost their geometric structure in the second film. Second, comparison of the predicted dynamic modulus and experimental data shows that i) strong interactions exist between PS nodules unless their coalescence has occured, leading to an abnormally high modulus at room temperature, ii) after achieving their coalescence, PS forms a more or less continuous phase. Both phenomena strongly depend on the particle size and their respective volume fractions.     

Supramolecular structures based on dimeric combinations of cyclodextrin and adamantane via click chemistry

The cyclic starches α-, β-, and γ-cyclodextrins (CDs) readily form inclusion complexes (ICs) with a large variety of polymers. In polymer-CD-ICs, the CD hosts are threaded by the guest polymers, which must be highly extended, and stacks of polymer threaded host CDs pack closely together and crystallize. When guest polymers are coalesced from their CD-IC crystals, by washing with a solvent good, bad for CD, polymer, or treatment with an amylase enzyme, the guest polymers coalesce into bulk samples whose structures, morphologies, and even conformations are distinct from bulk samples made from their solutions and melts. We generally observe (i) crystallizable homopolymers coalesced from their CD-ICs to evidence increased levels of crystallinity, unusual polymorphs, and higher melting, crystallization, and decomposition temperatures, while coalesced amorphous homopolymers exhibit higher glass-transition temperatures, than samples consolidated from their disordered solutions and melts; (ii) molecularly mixed, intimate blends of two or more polymers that are normally believed to be immiscible can be achieved by coalescence from their common CD-IC crystals, (iii) the phase segregation of incompatible blocks can be controlled (suppressed or increased) when block copolymers are coalesced from their CD-IC crystals, and (iv) the thermal and temporal stabilities of the coalesced and well-mixed homopolymer blends and block copolymers appear to be substantial, thereby suggesting retention of as-coalesced structures and morphologies under normal thermal processing conditions. Furthermore, CDs may be covalently incorporated in polymers both during and after their syntheses, thereby providing a broad range of new functionalities for delivery of additives or to act as sensors or filters. Alternatively, additive-CD-ICs or additives rotaxanated with CDs may be effectively delivered to polymers. As an example, TiO₂—filled polypropylene fibers may be readily dyed in aqueous solution using water soluble CD-rotaxanated azo-dyes.     

丙烯酸酯共聚物无皂水溶胶稳定性的研究

用溶液聚合法合成了四种AA含量不同的丙烯酸酯共聚物(MMA/BA/HEMA/AA)，通过中和AA使共聚物带有—COO~-能起自乳化作用分散于水中而成为无皂水溶胶．TEM观察表明水溶胶粒子呈球状，单分散性好，粒径随AA含量增加而变小，在30～90 nm范围．用电导滴定法测定水溶胶粒子中—COOH和—COO~-的分布，表明绝大部分—COO~-处于粒子表面，并且随AA含量增加，粒子表面的—COO~-增多，Zeta电位增大，这是导致水溶胶的抗电解质稳定性(以C.C.C.值反映)和贮存稳定性(以表现粘度反映)随AA含量增加而提高的主要原因。     

On the origin of colloidal particles in the dispersion polymerization of aniline

When aniline is oxidized in an aqueous medium in the presence of a steric stabilizer, colloidal polyaniline (PANI) dispersions are obtained. The generally accepted model of the stabilization assumes that the macromolecules of the water-soluble steric stabilizer are adsorbed at the polymer, precipitating during the dispersion polymerization, and provide steric protection against further aggregation. An alternative mechanism of conducting-polymer particle formation is proposed in the present study. We suggest that the steric stabilizer provides a site for adsorption of oligoaniline initiation centers; subsequent polymerization from anchored centers yields particle nuclei that grow to produce colloidal PANI particles. This hypothesis is based on the observation that the colloidal particles are obtained only in the case where the steric stabilizer is introduced in the early stages of polymerization when aniline oligomers are present in the reaction mixture. If the stabilizer had been added during the growth of PANI chains, colloidal dispersions would not have been produced. The process of particle growth is completely analogous to the formation of conducting PANI films on the surface of microparticles and various materials. There, the polymerization of aniline at the surfaces is preferred to the same process proceeding in the bulk of the reaction mixture. While the films grow at the interfaces with the reaction mixture, the dispersion particles similarly emanate from the stabilizer chains. The particle size, the formation of nonspherical morphologies, the importance of the chemical nature of the stabilizer chains, and the general relation between the conducting-polymer film and particle growth are discussed in the light of the proposed model.     

Reorganization of the structures,morphologies, and conformations of polymers by coalescence from their crystalline inclusion compounds formed with cyclodextrins

We and several other research groups have recently reported the ability of cyclodextrins (CDs) to act as hosts in the formation of inclusion compounds (ICs) with guest polymers. Polymer-CD-ICs are crystalline materials formed by the close packing of host CD stacks, which results in a continuous channel of ∼5-10Å in diameter running down the interior of the CD stacks. The guest polymers are confined to the narrow, continuous CD channels, and so are necessarily highly extended and segregated from neighboring polymer chains by the walls of the CD stacks. We have shown that coalescence of guest polymers from their CD-IC crystals can result in a significant reorganization of the structures, morphologies, and even conformations that are normally observed in their bulk samples. For example, when poly(ethylene terephthalate) (PET) is coalesced from its γ-CD-IC, we find that in the non-crystalline regions of the sample the PET chains are adopting highly extended kink conformations, which result in their facile recrystallization from the melt and prevent quenching of the coalesced PET to achieve an amorphous sample during rapid cooling from above T_m. We have also created well-mixed blends of normally incompatible polymers by coalescing them from CD-ICs containing both polymers, where they are necessarily spatially proximal. Finally we have found the unique morphologies created by the coalescence of homopolymers, block copolymers, and homopolymer pairs from their CD-ICs are generally stable to heat treatment for substantial periods above their T_m's and/or T_g's, and so may be thermoplastically processed without loss of the unique morphologies achieved through coalescence from their CD-IC crystals.     

Preparation of well-defined core-shell particles by Cu2+-mediated graft copolymerization of methyl methacrylate from bovine serum albumin

Small well-defined core-shell poly(methyl methacrylate)-bovine serum albumin (PMMA-BSA) particles have been prepared in a direct one-step graft copolymerization of MMA from BSA at 75 degrees C in water with a trace amount of Cu2+ (5 microM). Initially, BSA generates free radicals and acts as a multifunctional macroinitiator, which leads to the formation of an amphiphilic PMMA-BSA grafting copolymer. Such formed copolymer chains act as a polymeric stabilizer to promote further emulsion polymerization of MMA inside, resulting in surfactant-free stable core-shell particles, confirmed by a transmission electron microscopic (TEM) analysis. The PMMA-BSA copolymers as well as PMMA homopolymer inside the particles were isolated by Soxhlet extraction and characterized by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetry (TG). The highest grafting efficiency was approximately 80%. Effects of the reaction temperature, the MMA/BSA ratio, and the concentrations of Cu2+ and BSA on such core-shell particle formation have been systematically studied. Due to their inert PMMA core and biocompatible BSA shell, these small polymer particles are potentially useful in biomedical applications.     

液化膜对胶体悬浮液粘度的影响

Viscosity is one of the most important properties of colloids in mixing, transportation, stabilization, energy consumption, and so on. According to Einstein‘s viscosity equation, the viscosity of a colloidal dispersion increases with the increase of particle concentration. And the equation can be applicable to all micro-particle dispersions, because the effect of solvation films coated on particles can be neglectable in that case. But with the decrease of particle size to nano-scale, the formation of solvation films on nano-particles can greatly affect the viscosity of a dispersion, and Einstein‘s equation may not be applicable to this case. In this work, one kind of micro-size silica particle and two kinds of nano-size silica particles were used to investigate the effect of solvation films on dispersion viscosity, dispersed in water and ethyl alcohol solvents, respectively. The results of theoretical calculation and experimental investigation show that the increase of viscosity is contributed from solvation films by more than 95 percent for nano-particle dispersions, while less than 10 percent for micro-particle dispersions.     

SEP对PP/PS共混物的增容作用

研究了苯乙烯 -乙烯 /丙烯二嵌段共聚物 (SEP)对聚丙烯 /聚苯乙烯 (PP/PS)共混物的形态和力学性能的影响。结果表明 ,SEP在PP/PS共混物中作为增容剂 ,降低了分散相的聚结 ,减小了分散相的平均粒子尺寸 ,大大改变了共混物的形态 ,提高了共混物的力学性能 ,对PP/PS( 2 0 /80 )共混物的增容作用较为显著     

Small-angle neutron scattering on a core-shell colloidal system: a contrast-variation study

Small-angle neutron scattering (SANS) measurements are reported on a sterically stabilized, core-shell colloidal system using contrast variation. Aqueous dispersions of polystyrene particles bearing grafted poly(ethylene glycol) (PEG) have been studied over a large range of particle concentrations and two different solvent conditions for the PEG polymer. SANS data are analyzed quantitatively by modeling the particles as core-shell colloids. In a good solvent and under particle contrast conditions, an effective hard-sphere interaction captures excluded-volume interactions up to high concentrations. Contrast variation, through isotopic substitution of both the core and solvent, expedite a detailed study of the PEG layer, both in the dilute limit and as a function of the particle concentration. Upon diminishing the solvent quality, subtle changes in the PEG layer translate into attractions among particles of moderate magnitude.     

Self-emulsifying Hydroxy Acrylic Polymer Dispersions for Two Component Waterborne Polyurethane Coatings

Novel self-emulsifying acrylic polymer aqueous dispersions (NPAD) for two component waterborne polyurethane coatings (2K-WPU) were prepared by the emulsification of self-emulsifying polymer blends in water, which the polymer blends typically consist of two acrylic polymers, one is a salt group containing polymer (P1), the other is a polymer without salt groups (P2). The dynamic light scattering (DLS) analysis showed that the NPAD have a bimodal particle size distribution and the particle diameters can be controlled by the amount of salt group containing polymer and the concentration of salt groups in this polymer. Transmission electron microscopy (TEM) images also testified that the NPADs possess small particles consisted of P1 and core-shell structure large particles which are composed of the P1 in the shell parts and the P2 in the core parts. The property comparisons of the NPAD, conventional polyacrylic dispersion (CPAD) and poylacrylic emulsion (PAE) for 2K-WPU disclosed that the NPADs possess higher solid contents up to 45 wt% and much lower carboxy salt contents than those of the CPAD, and the NPAD-based 2K-WPU films display much better performance including 90% of the gloss, 0.81 of the pendulum hardness, much better solvent- and water-resistance than those of the CPAD and PAE. The TGA curves indicated the NPAD-based 2K-WPU films display good thermal stability.     

Synthesis and characterization of NiSn colloids and active solids prepared in organic solvents by CLD

Bimetallic colloidal dispersions were obtained by simultaneous cocondensation of nickel and tin atoms with organic solvents at 77 K using the chemical liquid deposition (CLD) method. The atoms in a 1:1 ratio were produced by resistive heating and were reacted with 2-propanol, 2-methoxyethanol, and acetone to produce colloids.The kinetic stability of the colloid dispersions was related to the solvation effect of organic molecules, e.g., low stability for acetone, higher for 2-propanol, and the highest for 2-methoxyethanol. The colloidal particles were characterized by UV-Vis measurements showing absorption bands at 204 and 270 nm. A 3-day study in which samples were taken every hour showed that the absorption bands decrease probably due to clustering. Electrophoretic measurements revealed that the particles are weakly positively charged. Transmission electron microscopy studies revealed an average particle size distribution ranging from 6 to 10 nm depending on the solvent. Most of the colloids exhibit a spherical shape with some degree of agglomeration.After solvent evaporation several active solids were obtained. The FTIR spectra show the presence of the solvent incorporated in the active solids/films, e.g., for acetone the carbonyl stretching is observed at 1723 cm^–1. The thermal stability of these bimetal powders/films was studied by TGA up to 550 °C. Their maximum decomposition temperatures are 350, 415, and 429 °C for NiSn–2-methoxyethanol, –2-propanol, and –acetone, respectively.