The aggregation behavior between anionic carboxymethylchitosan and cetyltrimethylammonium bromide: MesoDyn simulation and experiments

The aggregation behavior between carboxymethylchitosan (CMCHS) and cetyltrimethylammonium bromide (CTAB) is investigated by MesoDyn simulation and experimental techniques, for increasing CTAB concentrations. Mixed CMCHS/CTAB bulk aggregates are formed in the solution. Simulation results give the morphologies of aggregates clearly and illustrate the two stages for the formation of aggregates: the first stage is CTAB molecules aggregating on the CMCHS chain and the second stage is the equilibrium stage. A viscosity maximum and a hydrodynamic radius minimum at a certain CTAB concentration reveal the bridging structure of the polymer chains by the micelles. Transmission electron microscopy (TEM) images give the bridging structure clearly. At higher surfactant concentrations, light scattering and TEM show the existence of larger structures, whose size increases with CTAB concentration. According to the simulation and experimental results, the process of aggregate formation and aggregation mechanism are analyzed. Initially CMCHS and CTAB form network structure due to the bridge action of CTAB micelles, while the network structure disappears gradually and is replaced by ellipsoidal CMCHS/CTAB aggregate structure with CTAB concentration increasing.     

Topological building blocks of hydrogen bond network in water

Basic three-dimensional units of the network, called fragments, are introduced to characterize the hydrogen bond (HB) network structure of water. Topological differences among normal liquid water, water at low temperature, and water under high pressure are elucidated by their fragment statistics. Water at low temperature has almost defect-free network and is filled with stable fragments with small distortion. It is found that there exists a certain way on how fragments mutually aggregate. Well-formed aggregates heterogeneously constitute very stable network structures. HB network rearrangements occur scarcely inside these aggregated domains but take place in their surface areas. The heterogeneity of HB structure and rearrangement in water is thus explained in terms of the fragment structure and its rearrangements. The fragment analysis thus elucidates the intermediate-range order in water HB network.     

Real space structure of opaque gel

The structure of the opaque poly(acrylamide) gels is studied by using a confocal laser scanning microscope. The polymer network of the gel consists of the fractal aggregate of the colloidal particles in the higher concentration region of the cross-linker. The diameter of the colloidal particle, which formed in the gel, increases from 180 to 420 nm with an increase of the concentration of cross-linker. On the other hand, the fractal dimensions of the aggregate remain constant, ranging from 1.5 to 1.7. The densities of the particle are calculated to be 0.7 and 1.2 x 103 kg/m3, which are >10 times larger than the average density of the polymer network of the gel. The results indicate that the monomer and the cross-linker are densely cross-linked into the particles.     

Viscoelastic properties of ionic polymer composites reinforced by soy protein isolate

Both linear and nonlinear viscoelastic properties of ionic polymer composites reinforced by soy protein isolate (SPI) were studied. Viscoelastic properties were related to the aggregate structure of fillers. The aggregate structure of SPI is consisted of submicron size of globule protein particles that form an open aggregate structure. SPI and carbon black (CB) aggregates characterized by scanning electron microscope and particle size analyzer indicate that CB aggregates have a smaller primary particle and aggregate size than SPI aggregates, but the SPI composites have a slightly greater elastic modulus in the linear viscoelastic region than the CB composites. The composite containing 3–40 wt % of SPI has a transition in the shear elastic modulus between 6 and 8 vol % filler, indicating a percolation threshold. CB composites also showed a modulus transition at <6 vol %. The change of fractional free volume with filler concentration as estimated from WLF fit of frequency shift factor also supports the existence of a percolation threshold. Nonlinear viscoelastic properties of filler, matrix, and composites suggested that the filler‐immobilized rubber network generated a G′ maximum in the modulus‐strain curves and the SPI formed a stronger filler network than the CB in these composites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3503–3518, 2005     

Friction coefficient and structural transition in a poly(acrylamide) gel

The friction coefficient between the polymer network of an opaque poly(acrylamide) gel and water is measured as a function of the mole fraction of cross linker. The friction coefficients of opaque gels are 4 to 5 orders of magnitude smaller than those of the transparent gels. This drastic decrease in friction occurs when the mole fraction of cross linker is 0.2. In opaque gels, the friction coefficient of gels and the mole fraction of cross linker are related by a power law. The network structure of the opaque gels used in the friction measurements is examined with a confocal laser scanning microscope. The opaque gel network consists of a fractal aggregate of colloidal particles. The radius of particles and the volume occupied by the particles depend on the mole fraction of cross linker. Both relationships are well described by the power laws. The power law of the friction coefficient is well explained in terms of the power laws of the structural parameters and the Stokes equation of the hydrodynamic friction for the spherical particle. It indicates that the friction of the opaque gel is determined simply by the structure of the polymer network.     

Fractal Study of Mesoporous Structure in Water Molecular Condensed System

Bis-(4-stearoylaminophenyl) ether (BSADE) can aggregate and self-assemble in water. Transmission electron microscopy (TEM) indicated that the morphology of BSADE aggregates in water was entanglement and thin fiber-like, and that a three dimensional network structure was formed. Water molecules were entrapped in this three dimensional network structure and formed a new type of condensed system (so-called water molecular gel). Water molecular gel is a typical mesoporous material which can be characterized by the fractal dimension D. Using gas adsorption method along with measurement of porosity and specific surface area, the fractal dimension D of the complicated pores was 2.1-2.2 for this water molecular gel. Using viscosity method and the Cayley fractal tree, the fractal dimension D of the fiber-like three dimensional network was determined to be 1.98. The formation process of water molecular gel can be described as nucleation followed by a repeated growing and branching cycle.     

改性聚丙烯酰胺水溶液的疏水缔合性质

合成了一种疏水缔合水溶性聚丙烯酰胺共聚物,使用荧光光谱法并结合紫外及流变性实验,对制备的疏水缔合水溶性聚丙烯酰胺共聚物在水溶液中形成疏水微区、超分子聚集体及空间网络结构进行了研究,并用扫描电子显微镜证实了溶液中网络结构的存在.     

Hexagonal prismatic dodecameric water cluster: a building unit of the five-fold interpenetrating six-connected supramolecular network

An experimental (H(2)O)(n) (n > 10) aggregate, similar to a theoretical hexagonal prismatic dodecameric water cluster structure, is characterized, the water cluster can be reversibly generated. The hydrogen bonds between the water clusters and bis(imidazolyl) ligand result in the formation of a five-fold interpenetrating six-connected supramolecular network.     

Solution behavior of rod-like polyelectrolyte-surfactant aggregates polymerized from wormlike micelles

The behavior of a rod-like, water-soluble, polyelectrolyte-surfactant aggregate system (pC16TVB) in aqueous solution is characterized to determine the partitioning of surfactant in these systems and the impact on aggregate structure. These aggregates are generated by in situ polymerization of a cationic surfactant-hydrotrope wormlike micelle system. This system differs from most other polyelectrolyte-surfactant systems in that the monomer groups and the surfactant are present in ion pairs in the absence of added salts or counterions, so the stoichiometry (with respect to charge) is 1:1 for the system. Therefore, after polymerization the surfactant acts as the counterion for the polyelectrolyte chains as other counterions (salts) are not available. Despite being present in a 1:1 molar ratio, the aggregates are surprisingly stable in water (concentrations >600 mg/mL have been achieved). The conformation of the polyelectrolyte in the aggregate is analogous to the case of a polymer chain in tight confinement in a "tube" or cylindrical pore in which the pore walls are attractive--the tube is formed by the surfactant which is free to dissociate from the aggregates. A simple model for the structure and partitioning is presented and the ability to manipulate the aggregate structure is demonstrated.     

Colloid aggregation arrested by caging within a polymer network

The aggregation of colloidal particles within the confines of a polymer network has been studied. An isorefractive covalently cross-linked polymer gel in dimethyl sulfoxide was formulated so that the multicomponent system that is the gel is essentially invisible to light scattering. The high dielectric solvent was chosen so that electrostatics could be used to control the state of aggregation of a colloid dispersed within the gel matrix. Smoluchowski's population balance equations were solved for the case where aggregates larger than the gel's mesh spacing are immobile. Light scattering intensities predicted from the evolution of the aggregate population were calculated. The observed asymptotic increase in scattering intensity is consistent with this model and indicates that the aggregation process becomes arrested by the spatial constraints imposed by the mesh of the polymer network. Essentially once the aggregates reach a certain size, they become caged within the mesh of the gel network and thus no longer aggregate. Evidence is also given that indicates that formulating for specific gel properties can lead to controlled final aggregate size.     

Inorganic-organic hybrid nanoparticles from n-octyl triethoxy silane

Ormosil (organically modified silane) such as n-octyl triethoxy silane has been found to aggregate in the form of normal micelles as well as reverse micelles in which the triethoxy silane moeities are hydrolyzed to form a hydrated silica network while the n-octyl groups are held together through hydrophobic interaction. These nanoparticles are spherical in shape and are nearly monodispersed with an average diameter of below 100 nm. The nanoparticles originating from the micellar aggregate have an hydrophobic core with a layer of the hydrated silica network at the surface. The hydrophobic core can host hydrophobic molecules such as tetraphenyl porphyrin, which is leached out of the particles extremely slowly compared to that in Triton X-100 micelles. The nanoparticles originating from the reverse micelles have a hydrated silica network in the core surrounded by the hydrophobic n-octyl chains on the particle surface. The hydrophilic silica cores of these nanoparticles have been used to encapsulate horseradish peroxidase (HRP) and the enzyme shows its activity and follows Michaelis-Menten kinetics.     

Phosphorescent platinum acetylide organogelators

The series of platinum acetylide oligomers (PAOs) with the general structure trans,trans-[(RO)3Ph-C[triple bond]C-Pt(PMe3)2-C[triple bond]C-(Ar)-C[triple bond]C-Pt(PMe3)2-C[triple bond]C-Ph(OR)3], where Ar = 1,4-phenylene, 2,5-thienylene, or bis-2,5-(S-2-methylbutoxy)-1,4-phenylene and R = n-C12H25 gel hydrocarbon solvents at concentrations above 1 mM. Gelation is thermally reversible (T(gel-sol) approximately 40-50 degrees C), and it occurs due to aggregation of the PAOs resulting in the formation of a fibrous network that is observed for dried gels imaged by TEM. The influence of aggregation/gelation on the photophysical properties of the PAOs is explored in detail. Aggregation induces a significant blue shift in the oligomers' absorption spectra, and the shift is attributed to exciton interactions arising from H-aggregation of the chromophores. Strong circular dichroism (CD) is observed for gelled solutions of a PAO substituted with homochiral S-2-methylbutoxy side chains on the central phenylene unit. The CD is attributed to formation of a chiral supramolecular aggregate structure. The PAOs are phosphorescent at ambient temperature in solution and in the aggregate/gel state. The phosphorescence band is blue-shifted ca. 20 nm in the aggregate/gel, and the shift is assigned to emission from an unrelaxed conformation of the triplet excited state. Phosphorescence spectroscopy of mixed aggregate/gels consisting of a triplet donor/host oligomer (Ar = 1,4-phenylene) doped with low concentrations of an acceptor/trap oligomer (Ar = 2,5-thienylene) indicates that energy transfer occurs efficiently in the aggregates. Triplet energy transfer involves exciton diffusion among the host chromophores followed by Dexter exchange energy transfer to the trap chromophore.     

CMC系列高分子表面活性剂的胶束形态

高分子表面活性剂分子量高 ,分子中兼具亲水和疏水链段 ,在选择性溶剂水中同小分子表面活性剂一样 ,可形成疏水链段为核心、亲水链段为外壳的胶束结构 ,但高分子量又使其表现出许多不同于低分子表面活性剂的形态特征 ,如胶束的多种形态、尺寸分布多分散性等等 ,而这些形态特征对高分子表面活性剂的界面活性、增粘、乳化等性能有决定性的影响．结构规整的嵌段或接枝共聚物在选择性溶剂中的分子聚集形态已有研究 ［１,２］,亲水亲油性的高分子表面活性剂在水溶液中由于结构复杂、水溶液中氢键作用及静电作用力等因素造成的困难 ,因而研究较少…     

INTERACTIONS BETWEEN CATIONIC STARCH AND ANIONIC SURFACTANTS III RHEOLOGY AND STRUCTURE OF THE COMPLEX PHASE

This paper reports on studies of the rheological properties of cationic starch (CS)/ surfactant systems. The degree of substitution of the CS was 0.1 - 0.8. Surfactants investigated were sodium dodecyl sulfate (SDS), potassium octanoate (KOct), sodium decanoate (NaDe)potassium dodecanoate (KDod), sodium oleate (NaOl) and sodium erucate (NaEr). Aggregation of surfactant micelles with the polymer produces a hydrophobic and pseudoplastic gel-like complex phase with low water content and high viscosity. The rheological behavior of the gels is described by the Herschel-Bulkley model. In dilute aqueous solution the CS/surfactant aggregate structure resembles a randomly coiled polymer network, in which polymer molecules are linked by micelles. The rheological data for the gel are compatible with the assumption that the surfactants form liquid crystalline structures with the polymer anchored to the surfactant aggregates, as recently suggested for analogous systems. However, this conjecture needs to be corroborated by more direct determinations of the structure.     

Self-assembled nanowire networks of aryloxy zinc phthalocyanines based on Zn-O coordination

Tetrakis(aryloxy)phthalocyanine (4c) and its Zn congeners (4a and 4b) and Ni congener (4d) were synthesized, and their self-assembling properties in coordinating and non-coordinating solvents were investigated by absorption and fluorescence spectroscopy, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), and transmission electron microscopy (TEM). Compounds 4a and 4b in non-coordinating solvents exhibit red-shifted and split Q-bands in absorption spectra even at very low concentrations, suggesting J-aggregate formation. The MALDI-TOF MS for the samples of 4a and 4b prepared from chloroform solutions gives the monomer and aggregate signals. The TEM images of such samples display an indefinite two-dimensional network structure. The aggregates break up into monomers when a coordinating solvent is added to the solution. The driving force for the aggregate formation is proposed to be the complementary coordination of the ether oxygen in the aryloxy groups of one molecule to the core Zn of another molecule of phthalocyanine.     

Aggregation Behavior of Cationic Copolymer Methacryloxyethyl Trimethyl Ammonium Chloride‐Butyl Acrylate‐Acrylamide in Aqueous Solution

The aggregation behavior of cationic copolymer methacryloxyethyl trimethyl ammonium chloride‐butyl acrylate‐acrylamide (MTAC‐BA‐AM) was investigated via surface property and fluorescence spectroscopy measurements, as well as Mesodyn simulation, etc. The experimental results indicate that MTAC‐BA‐AM has the ability for decreasing surface tension of water and there are two break points in the surface tension isotherm; and its surface dilational viscoelasticity and apparent viscosity in aqueous solution depend upon aggregate structure. The Mesodyn simulation results show that spherical, cylindrical aggregates, and network structures form in aqueous solution with the concentration increasing. The aggregation process is driven by enthalpy and can be divided into two stages. The first stage is controlled by diffusion, while the second one is controlled by hydrophobic interaction.     

Research on Configuration of Polymer Molecular Aggregate and Its Reservoir Applicability

This article researches the effect of configuration of polymer molecular aggregate on the performance of polymer solution and its reservoir applicability, taking configuration of polymer molecular aggregate, first normal stress difference, resistance coefficient, residual resistance coefficient, and oil recovery as the evaluation indexes, guided by physical chemistry, polymer materials science, and reservoir engineering, by means of chemical analysis, instrument detection, and physical simulation. Results show that the apparent viscosity of polymer solution is closely related to the configuration of molecular aggregate. However, that reflects neither the transporting and migrating ability of molecular aggregate in porous media nor the applicability of polymer solution for reservoir core pore. Compared with “linear-branched chain” polymer, network polymer has a regional “laminated-net” structure, which has a stronger ability to adsorb and wrap hydrone, when deformation occurs, internal friction of which is larger, and apparent viscosity of which is higher with isoconcentration. Changing the configuration of molecular aggregate can enhance the tackify performance of polymer, but crosslinking or association degree must be controlled properly. Otherwise, the applicability of polymer solution for reservoir core pore will become poor, thus influencing the oil incremental effect of polymer flooding.     

Deposition of spherical particles onto cylindrical solid surfaces. I. Numerical simulations

The permeability of fractal porous aggregates with realistic three-dimensional structure is investigated theoretically using model aggregates composed of identical spherical primary particles. Synthetic aggregates are generated by several techniques, including a lattice-based method, simulation of aggregation by differential settling and turbulent shear, and the specification of simple cubic structures, resulting in aggregates characterized by the number of primary particles, solid fraction, characteristic radius, and fractal dimension. Stokesian dynamics is used to determine the total hydrodynamic force on and the distribution of velocity within an aggregate exposed to a uniform flow. The aggregate permeability is calculated by comparing these values with the total force and velocity distribution calculated from the Brinkman equation applied locally and to the entire aggregate using permeability expressions from the literature. The relationship between the aggregate permeability and solid fraction is found to be best predicted by permeability expressions based on cylindrical rather than spherical geometrical elements, the latter tending to underestimate the aggregate permeability significantly. The permeability expressions of Jackson and James or Davies provide good estimates of the force on and flow through porous aggregates of known structure. These relationships are used to identify a number of general characteristics of fractal aggregates.     

Structural rearrangement and stiffening of hydrophobically modified supramolecular hydrogels during thermal annealing

Dynamic crosslinks formed by thermoreversible associations provide an energy dissipation mechanism to toughen hydrogels. However, the details of the organization of these crosslinks impact the hydrogel properties through constraints on the network chain conformation. The physical crosslinks generated by hydrophobic association of the 2‐(N‐ethylperfluorooctane‐sulfonamido)ethyl methacrylate (FOSM) groups in a random copolymer of N,N‐dimethylacrylamide (DMA) and FOSM provide a simple system to investigate how the hydrogel structure (as determined from small angle neutron scattering impacts the mechanical properties of the hydrogel. The initial hydration of the copolymer at 25 °C leads to a kinetically trapped structure with large‐scale heterogeneities. Heating the hydrogel at 60 °C, which is above the glass transition temperature for the FOSM domains, allows the hydrogel structure to rearrange to reduce the density of network defects and the structural heterogeneities. That effectively increases the crosslink density of the network, which stiffens the hydrogel and decreases the swelling at equilibrium at 25 °C. The processing history determines how the hydrophobes aggregate to form the physically crosslinked network, whose structure defines the mechanical properties of these hydrogels. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1036–1044     

J-aggregates prepared by adsorption at monolayer/water interfaces

By adsorption of anionic cyanine dyes at positivly charged lipid monolayers large J-aggregates are formed. Absorption and fluorescence spectra are measured at the air/water interface during the crystallization process. The influence of the lipid/dye interaction on the aggregate structure is studied for two different systems. It is shown that the aggregate structure can be improved by growing crystals from a seed.