Determination and comparison of molar mass distributions of substituted polystyrenes and block copolymers by using thermal field-flow fractionation, size exclusion chromatography and light scattering (2023)

Field-flow fractionation (FFF) is a family of analytical techniques developed specifically for separating and characterizing macromolecules, supramolecular assemblies, colloids and particles. It combines the effects of a laminar flow profile with an exponential concentration profile of analyte components caused by their interactions with a physical field applied perpendicular to the flow of a carrier liquid. FFF is undergoing increasingly widespread use as researchers learn of its potential and versatility. This overview underlines the basic principle and theory behind FFF and reviews recent research efforts incorporating flow and thermal FFF methods to characterize natural, biological, and synthetic polymers. These FFF techniques will be discussed in terms of theory and practice. Selected applications of FFF and their coupling capability with other chromatographic techniques or spectrometric detection for the separation and characterization of polymers in organic and aqueous media are presented.

Science Bulletin, Volume 60, Issue 10, 2015, pp. 936-942

Based on the noncovalent functionalization of ferrocene-grafted polyethylenimine (PEI-Fc) and carbon nanotubes (CNTs), CNT bundles are exfoliated by PEI-Fc solution and thus form stable compounds [emailprotected], which is used to construct the [emailprotected]/DNA multilayers through layer-by-layer assembly. The multilayers show a highly uniform and homogeneous characteristic, which significantly improve the electrical property of the multilayers. Upon the oxidation electrical potential, the ferrocene groups are switched from reduction state ([Fe(C₅H₅)₂]) to oxidation state ([Fe(C₅H₅)₂]⁺), leading to change of microenvironments’ charge density, resulting in swelling of the multilayers and a final degree of swelling of 37% and the decrease of multilayer stiffness. We maintain that electrochemical control over the swelling behavior of multilayers could have important implications for responsive coatings of nanoscale devices, including mechanically tunable surfaces which are used to modulate cellular activities and control drug delivery.

Polymer, Volume 92, 2016, pp. 13-17

Homogeneous polymer hybrid consisting of poly(β-alanine) and silica gel was synthesized by an in-situ anionic polymerization method. Acrylamide (AAm) as an organic monomer was introduced into a sol–gel reaction of tetramethoxysilane (TMOS). The polymerization of AAm was initiated by potassium tert-butoxide (t-BuOK), while sol–gel reaction of TMOS proceeded to generate a silica gel matrix. The obtained polymer hybrid was optically transparent and no phase separation was observed by SEM measurement. From the ¹H and ¹³C NMR analysis, the anionic polymerization of AAm proceeded via a hydrogen-transfer process under in-situ hybridization conditions.

Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volume 498, 2016, pp. 112-120

Interpolyelectrolyte complexes (IPEC) have been used in different fields, ranging from biomedicine to oil exploration. Particle dimension is a key parameter for the use of an IPEC for a particular application. In this work, dynamic and static scattering (in the form of optical DLS and SAXS, respectively) were used to follow particle growth as a function of anionic/cationic polyelectrolyte mass ratio, $w_{AC}$, coupled to turbidimetry, conductometry, viscometry, and zeta potential measurements. Turbidimetry, conductometry, and viscometry showed that at $w_{AC}\cong 2$ the IPEC dispersions presented changes that were associated to a massive production of IPEC particles. At the same $w_{AC}$ value, zeta potential measurements indicated an apparent isoelectric point, showing that this $w_{AC}$ must be related to a stoichiometric point for IPEC formation. Double KWW equation was adjusted to data from DLS intensity correlation functions, and parameters related to the distribution of relaxation rates presented characteristic changes at the same value of $w_{AC}$. SAXS was used to follow particle growth until massive IPEC production. It showed that particles firstly were in the form of small, globular particles, tending to unfolded chain geometry, which can be related to the occurrence of flocculation, just at the point of massive IPEC production.

European Polymer Journal, Volume 52, 2014, pp. 137-145

Nanostructured hydrogels tailor-made for specific applications are new grounds for the creation of novel soft materials. The current research presents a new method for hydrogel nanostructuring involving the incorporation of Pluronic® F127 micelles mixed with acrylated blockcopolymer molecules, which enable the attachment of these micelles to the hydrogel matrix through their endgroups. This design impacts the hydrogel nanostructure as well as its swelling and mechanical properties. Small Angle X-ray Scattering (SAXS) and Cryogenic Transmission Electron Microscopy (cryo-TEM) revealed that photochemical crosslinking of the hydrogel caused immobilization of the nanostructured micelles. Mechanical and weight gain experiments demonstrated a significant impact of these nanostructures on the hydrogel’s elastic modulus as well as the transient and equilibrium weight gain ability of the material.

Polymer, Volume 97, 2016, pp. 1-10

This study reveals the critical importance of dipole–dipole interaction for homopolymers to form self-assembled microspheres in solutions. For the polymers with different side-groups, the self-assembly is induced by gradually adding deionized water into their solutions in N, N-dimethylformamide (DMF). Three of the polymers containing side-groups with the strong dipoles form uniform colloidal spheres in the processes. Beyond the critical water content (CWC), the aggregate sizes first increase and then decrease with the increasing water content before forming the final assemblies. In the intermediate states, the aggregates possess a microgel-like structure in the swollen form. On the other hand, no such self-assembling behavior is observed for the other polymer without the dipolar side-groups, which precipitates from the DMF-H₂O solution with the increase in the water content. The strong dipolar groups acting as associating groups are necessary to avoid polymer molecules forming dense aggregates and precipitating from the solutions after phase separation.

Journal of Chromatography A, Volume 1367, 2014, pp. 90-98

New monolithic reversed-phase liquid chromatography (RPLC) stationary phases based on single multi-acrylate/methacrylate-containing monomers [i.e., 1,12-dodecanediol dimethacrylate (1,12-DoDDMA), trimethylolpropane trimethacrylate (TRIM) and pentaerythritol tetraacrylate (PETA)] were synthesized using organotellurium-mediated living radical polymerization (TERP), which was expected to produce more efficient monolithic columns than conventional free-radical polymerization. The rationale behind selection of porogens, relative concentrations of reagents and polymerization conditions are described. The new monolithic columns were applied to the separation of small molecules (i.e., alkylbenzenes) under isocratic conditions. Chromatographic efficiencies as high as 60,200plates/m (71,300plates/m when corrected for extra-column variance) were obtained, showing a general improvement over previous RPLC monoliths.