Formation Of Polymer Aggregates Research Articles

Polysaccharide derivative as an additive in Olefin-Based drilling fluid

The search for drilling fluids of low environmental impact and high performance has increased and became of utmost importance over the years. In this study, a hydrophobically modified polysaccharide was obtained from the reaction of carboxymethylcellulose (CMC) with dodecylamine (DDA) in water and evaluated as a new green additive in an olefin-based fluid. FTIR and 1H NMR spectra revealed the presence of amide groups on the CMA-DDA derivative, demonstrating that the reaction was successful. Unlike the polysaccharide precursor, the product showed turbidity in water, due to association between hydrophobic groups inserted onto CMC chains. The formation of polymer aggregates in water was confirmed by DLS. The rheological measurements in water and saline medium also corroborated to DLS data, as the viscosity of the derivative was higher than that of CMC. Confocal microscopy indicated that the hydrophobically modified CMC contributes to the inverse emulsion stability. CMC-DDA behaved as an efficient rheological modifier on olefin-based drilling fluids, besides of contributing to reduce filtrate loss under high temperature and high pressure (HTHP) conditions.

From blue fluorescence to red fluorescence: Solid-state oxidative coupling polymerization of fluorene and anthracene or naphthalene

Through the solid-state oxidative coupling polymerization, a series of fluorene-co-anthracene copolymer (PFA) and fluorene-co-naphthalene copolymers (PFN) were synthesized using FeCl3 as the oxidant. The structures of the copolymers were characterized by FT-IR and 1H NMR spectra, showing the random structures composed of fluorene units and 9,10-anthracene units or 1,4-linked naphthalene units. The increasing fluorene units in the backbones resulted in the increasing crystallization of copolymers by XRD patterns. All the copolymers exhibited good thermal stability. The optical properties could be adjusted by using different fluorene and anthracene or naphthalene ratios. Moreover, the polymer concentrations that affected the photoluminescence emission ranged from blue light to red light. The concentration-induced discoloration property also could be observed from the copolymers on the filter paper of TLC plates. This is attributed to the change in the effective conjugation length of a single polymer and the formation of polymer aggregates and excimers. These unique properties endow the PFA and PFN with potential applications in optoelectronics. Especially, these polymers exhibit enhanced emissions and on/off fluorescent switching which senses THF vapor efficiently.

Interaction of a Poly(phenylene vinylene) with an Organometallic Lewis Acid Additive: Fundamentals and Application in Polymer Solar Cells

The trimeric perfluoro-o-phenylene mercury compound Hg3 and poly(2-methoxy,5-(2′-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) interact strongly in solution and the solid state. The interaction is attributed to electron donor–acceptor complex formation, where MEH-PPV is the donor, and the Lewis acid Hg3 is the acceptor. The study reported herein explores the effects of the donor–acceptor complex formation on the properties of MEH-PPV in solution and in the solid state. Addition of Hg3 to MEH-PPV solution or films leads to a distinct color change, and the change in the visible absorption spectrum and fluorescence of MEH-PPV is consistent with the formation of polymer aggregates. In the solid state, Hg3 induced aggregation is suggested to lead to formation of crystalline domains of the conjugated polymer. Transmission electron microscopy and grazing incidence X-ray scattering results support the hypothesis that the complex formation with Hg3 induces aggregation of the polymer. Transient absorption spectros...

Photophysical properties of poly(phenylene-co-fluorene) synthesized via solid-state oxidative coupling polymerization

A series of benzene-co-fluorene copolymers were synthesized via solid-state oxidative coupling polymerization using FeCl3 as the oxidation catalyst. The structural characterization results confirm that the products are random copolymers composed of 1,4-linked phenylene units and 2,7-linked fluorene units. All the copolymers exhibited good thermal stability. The DSC and XRD results showed that the crystallization of copolymers increased with the increasing fluorene units in the backbones. The relationships among molecular structure, condensed-state structure, and photophysical properties of these polymers were investigated by UV–vis absorption spectroscopy and photoluminescence spectroscopy. The optical properties could be adjusted by using different ratios of fluorene and dibutoxybenzene. Moreover, the polymer concentrations and states affected the emission properties of copolymers. This can be attributed to the change in the effective conjugation length of single polymer and the formation of polymer aggregates and excimers. These unique properties endow the benzene-co-fluorene copolymers with potential applications in optoelectronics.

Concentration-induced discoloration properties of poly(alkoxynaphthalene)s synthesized by solid-state oxidative coupling polymerization

Poly(alkoxynaphthalene)s were synthesized by grinding 2-alkoxynaphthalenes with FeCl3 as the oxidant at room temperature via solid-state oxidative coupling polymerization. Based on the structural characterization and analysis, the condensed structure of 1,4-linked polynaphthalenes is the dominant structure of the polymer, accompanied with the formation of intramolecular coupling. The polymers not only exhibit perfect heat-resistant property, but also show the concentration-induced discoloration property. With the continuously increasing polymer concentrations, the maximum fluorescence bands were observed from the ultraviolet region to 520nm, eventually red shifting to 620nm at the polymer concentration above 0.1mgmL−1. Moreover, the choice of solvent and the extended side-chains can affect the fluorescence spectral changes. In combination with the fluorescence spectral changes of poly(alkoxynaphthalene)s in PMMA films, the concentration-induced discoloration property is mainly dependent on a transition from twisted conformations to planar structures and the formation of polymer aggregates. Moreover, these polymers exhibit obvious enhanced emissions and on/off fluorescent switching which sense THF vapor. It is suggested that poly(alkoxynaphthalene)s are potential materials for fabrication of fluorescence sensors to detect THF efficiently.

The role of macromolecules in the formation of kidney stones.

The formation of crystal aggregates, one of the critical processes in kidney stone pathogenesis, involves interactions between crystals (predominantly calcium oxalate monohydrate, COM) and urinary constituents (e.g., proteins), which serve as an adhesive "glue" between crystals in stones. To develop a better understanding of the protein-crystal interactions that lead to crystal aggregation, we have measured the effect of model proteins on bulk COM crystal properties as well as their adsorption on crystal surfaces using three synthetic polyanions: poly(aspartic acid) (polyD), poly(glutamic acid) (polyE), and poly(acrylic acid) (polyAA). These anionic macromolecules reduced the amount of COM crystal aggregation in bulk solution to an extent similar to that observed for mixture of proteins from normal urine, with little difference between the polymers. In contrast, the polymers exhibited differences in measures of COM crystal growth. Polycations such as poly(arginine) (polyR) and poly(lysine) (polyK) reduced aggregation weakly and exerted negligible effects on crystal growth. All polyions were found to associate with COM crystal surfaces, as evidenced by changes in the zeta potential of COM crystals in electrophoretic mobility measurements. On the other hand, COM aggregation and possibly growth can be promoted by many binary mixtures of polycations and polyanions, which appeared to be mediated by polymer aggregate formation rather than loss of crystal charge stabilization. Similarly, crystal aggregation promotion behavior can be driven by forming aggregates of weakly charged polyanions, like Tamm-Horsfall protein, suggesting that polymer (protein) aggregation may play a critical role in stone formation. Sensitivity of polyanion-COM crystal surface interactions to the chemical composition of polymer side groups were demonstrated by large differences in crystal aggregation behavior between polyD and polyE, which correlated with atomic force microscopy (AFM) measurements of growth inhibition on various COM surfaces and chemical force microscopy (CFM) measurements of unbinding forces between COM crystal surfaces and AFM tips decorated with either carboxylate or amidinium moieties (mimicking polyanion and polyR side chains, respectively). The lack of strong interaction for polyE at the COM (100) surface compared to polyD appeared to be the critical difference. Finally, the simultaneous presence of polyanions and polycations appeared to alter the ability of polycations to mediate unbinding forces in CFM and promote crystal growth. In summary, polyanions strongly associated with COM surfaces and influenced crystallization, while polycations did not, though important differences were observed based on the physicochemical properties of polyanions. Observations suggest that COM aggregation with both polyanion-polycation mixtures and weakly charged polyanions is promoted by polymer aggregate formation, which plays a critical role in bridging crystal surfaces.

AFM images of the dark biocidal action of cationic conjugated polyelectrolytes and oligomers on Escherichia coli.

Polymers and oligomers with conjugated phenylene ethynylene or thiophene ethynylene backbones have been shown to be potent antimicrobials. The mechanisms by which they act have been unclear, though AFM imaging of Escherichia coli cells before and after exposure to two such biocides, PPE-Th polymer and EO-OPE-1(C3), shows their effects on cell surface structure. Dried, unexposed E. coli cells could be imaged at resolution high enough to discern the physical structure of the cell surfaces, including individual porin proteins and their distribution on the cell. Exposure to 30 μg/mL PPE-Th polymer caused major cell surface disruption due to either emulsification of the outer membrane or the formation of polymer aggregates or both. In contrast, exposure to 30 μg/mL EO-OPE-1(C3) oligomer did not cause large-scale membrane disruption but did cause apparent reorganization of the surface proteins into linear arrays or protein-lipid-OPE complexes that dominate on a small scale. E. coli cells were also successfully imaged underwater, allowing a real-time AFM image series as cells were exposed to 30 μg/mL EO-OPE-1(C3). Solution exposure caused the cell surfaces to noticeably increase their roughness over time. These results agree with proposed mechanisms for cell killing by PPE-Th and EO-OPE-1(C3) put forth by Wang et al.1 in which PPE-Th kills by large-scale disruption of the outer membrane and EO-OPE-1(C3) kills by membrane reorganization with possible pore formation.

Self-association behavior in water of an amphiphilic diblock copolymer comprised of anionic and dendritic blocks

Well-defined amphiphilic diblock copolymers (PAMPS-b-PG2) composed of a hydrophilic linear polyelectrolyte and hydrophobic blocks bearing pendent dendritic moieties was synthesized via reversible addition–fragmentation chain transfer (RAFT) controlled radical polymerization of 3,5-bis[3′,5′-bis(benzyloxy)benzyloxy]benzyl 11-acrylamidoundecanoate (G2) using a poly(sodium 2-(acrylamido)-2-methylpropanesulfonate) (PAMPS) based macro-chain transfer agent. Degrees of polymerization of PAMPS and PG2 blocks were 71 and 3, respectively. The polydispersity index was 1.25 as estimated from GPC. Hydrophobic association of the PG2 blocks in aqueous solutions was suggested from restricted motions of the dendritic moieties as observed by 1H NMR in D2O. A fluorescence spectrum of 8-anilino-1-naphthalenesulfonic acid, ammonium salt hydrate indicated that the fluorescence probe was solubilized in the hydrophobic domain formed from the polymer aggregate in water. The formation of polymer aggregates was indicated by light scattering data. The hydrodynamic radius (Rh) of the polymer aggregate was independent of the polymer concentration.

Nanoparticle-Assembled Capsule Synthesis: Formation of Colloidal Polyamine−Salt Intermediates

There is current interest in developing new synthesis strategies for multifunctional hollow spheres with tunable structural properties that would be useful in encapsulation and controlled release applications. A new route was reported recently, in which the sequential reaction of polyamines, multivalent anions, and charged nanoparticles leads to the formation of polymer-filled and water-filled organic/inorganic micron-sized structures known as nanoparticle-assembled capsules. This technique is unique among other capsule preparation routes, as it allows the rapid and scalable formation of robust shells at room temperature, in near-neutral water, and with readily available precursors. This nanoparticle assembly synthesis route involves two steps: the formation of polymer aggregates and the subsequent deposition of particles around the aggregates. The purpose of this paper is to understand in greater detail the noncovalent chemistry of the polymer-salt aggregation step. With poly(allylamine hydrochloride) (PAH) as the model polymer, aggregate formation was investigated as a function of charge ratio, pH, and time through dynamic light scattering, electrophoretic mobility measurements, chloride ion measurements, and optical microscopy. PAH formed aggregates by the cross-linking action of divalent and higher-valent anions above a critical charge ratio and in a pH range defined by the pKa values of PAH and the anion. The aggregates grew in size through coalescence and with growth rates that depended on their surface charge. Controlling polymer aggregate growth provided a direct and simple means to adjust the size of the resultant capsule materials.

Function and performance of silicone copolymer (VI). Synthesis and novel solution behavior of water-soluble polysiloxanes with different hydrophiles

Silicone surfactants containing different pendant hydrophilic groups such as diethanol tertiary amine (SHE, nonionic), diethanol methyl quaternary amine (cationic) and triethyl quaternary amine (cationic) have been synthesized and characterized by 1H and 13C NMR and gel permeation chromatography. The solution behavior of these novel surfactants has also been investigated by surface tension measurement and a fluorescence method. It has been observed that the surface tension of these surfactants decreases as a function of time at a very low polymer concentration (1 × 10−4 wt%). At higher concentration (0.1 wt%), the equilibrium surface tensions reached very low values compared to that of typical polymer surfactants, for example, poly(ethylene oxide–propylene oxide) block copolymer (EPE0.8). In addition, the low I 1/I 3 values of these silicone surfactants indicate the formation of polymer aggregates in aqueous solution, and an extremely low I 1/I 3 value of SHE (1.06) compared to other polymeric surfactants (EPE0.8) and conventional surfactants [poly(ethylene glycol n-nonyl phenyl ethers), cetyltrimethylammonium bromide, and sodium dodecyl sulfate] indicates its stronger hydrophobicity.

Shear thickening of halato-telechelic polymers in apolar solvents

Short-length polymers selectively end-capped with a metal carboxylato group at both ends, i.e. metal carboxylato-telechelic polymers, exhibit an unusual shear-thickening behaviour in apolar solvents, depending on the main experimental parameters that control the ion-pair association, such as metal cation, concentration and temperature. In contrast to the non-ionic precursors, metal carboxylato-telechelics are indeed responsible for a marked increase in the solution viscosity in a range of shear rates between 0.1 and 1000 s −1. The shear-rate dependence of the solution viscosity has been analysed in a close relationship to metal counterion, polymer concentration, temperature and addition of polar compounds to the apolar solvent. As a rule, the dilatant behaviour depends strongly on the formation of polymer aggregates in relation to the mutual interactions of the ion pairs. A consensus is now emerging on the origin of the shear-thickening effect, which should be found in inter-aggregate associations rather than in a transition from intramolecular to intermolecular associations of the individual chains.