Effects of Molecular Weight below the Entanglement Threshold on Interfacial Nanoparticles/Polymer Dynamics

Abstract

This work deals with effects of polymer molecular weight, W m, below the entanglement threshold, W m,e, on molecular dynamics of polydimethyl­siloxane (PDMS) adsorbed onto silica particles, employing differential scanning calorimetry (DSC) and two dielectric techniques: broadband dielectric spectroscopy (BDS) and thermally stimulated depolarization currents (TSDC). The rigid amorphous polymer fraction at interfaces, RAFint, was found suppressed for larger W m by all techniques in qualitative agreement with each other. Results on RAFint were supported by evaluating, for the first time, the coverage of hydroxyls at the surfaces of nanoparticles by polymer chains (S relaxation). The mobility of interfacial polymer (αint relaxation) was followed by BDS and TSDC, showing suppression of dynamics and cooperativity with decreasing W m. We suggest that interfacial polymer fraction and dynamics are dominated by the concentration of polymer–particle contact points, the latter increasing for smaller W m due to more free chain ends, as expected below W m,e. Furthermore, adopting models that describe multiple conformations for polymers adsorbed on solid surfaces, we explain our results in terms of promotion of tail/loop-like conformations in the particle–polymer interfacial layer for shorter/longer polymer chains, respectively. The model was further checked by employing surface modification of initial silica, which resulted in smoothening of nanoparticle surface and led to further suppression of RAFint and interfacial polymer dynamics.

Silica-supported $$\hbox {Ni}_{{x}}\hbox {O}_{{y}}$$, $$\hbox {Zn}_{{x}}\hbox {O}_{{y}}$$ and $$\hbox {Mn}_{{x}}\hbox {O}_{{y}}$$ nanocomposites: physicochemical characteristics and interactions with water and n-decane

“…During recent decades, nanocomposites based on a combination of two or more oxides of various metals or metalloids have had considerable interest due to their wide application possibilities in various fields of chemistry, physics, materials science and industry [1][2][3]. High dispersity of these oxides and the presence of various active surface sites are of importance for the use of them as sorbents [4,5], hetero catalysts with an adjustable set and activity of surface acid/base sites [6][7][8][9], fillers of polymers [10][11][12], etc.…”

Gels without Vapor Pressure: Soft, Nonaqueous, and Solvent‐Free Supramolecular Biomaterials for Prospective Parenteral Drug Delivery Applications

“…For example, Appel et al showed that in hydrogels formed via polymer/nanoparticle bridged flocculation interactions, the diameter of particles must be smaller than the persistence length of the polymer in order for percolation to occur . Similar to hydrated nanocomposites, percolation and stiffness of solvent‐free supramolecular nanocomposites are generally enhanced by smaller particle size, higher polymer molecule weight, and propensity of hydrogen bonding between the polymer chains and the surface of the nanoparticles …”

Polymer Adsorbents vs. Functionalized Oxides and Carbons: Particulate Morphology and Textural and SurfaceCharacteristics

“…Therefore, additional methods, such as small-angle X-ray or neutrons scattering (SAXS, SANS) [ 53 , 54 , 55 , 56 , 57 , 58 ], X-ray diffraction (XRD) [ 59 , 60 , 61 ], high-resolution transmission (HRTEM) and scanning (SEM) electron microscopies [ 59 , 62 ], nuclear magnetic resonance (NMR) spectroscopy with cryoporometry and relaxometry [ 15 , 63 , 64 , 65 ], differential scanning calorimetry (DSC) and thermoporometry [ 66 ], infrared spectroscopy (FTIR), thermogravimetry (TG) and thermoporometry, dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization current (TSDC) and relaxometry, theoretical simulations, etc. [ 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 ] should be used. Besides the textural characteristics, the data of these methods allow one to obtain information on the materials’ behavior under different conditions, which could model real situations related to practical applications.…”

“…To analyze these dependencies (typically complex for complex materials), certain model equations should be used and treated with the applied mathematics methods (used, e.g., to solve integral and differential equations, to minimize functionals, to regularize experimental noise effects, etc.) and related computer programs [ 3 , 4 , 5 , 6 , 7 , 8 , 31 , 32 , 53 , 54 , 55 , 56 , 63 , 64 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 ]. Even if the experimental methods give direct information (e.g., TEM, SEM) that certain computer methods and programs should be used to obtain quantitative characteristics, e.g., the particulate morphology, porosity, particle and crystallite size distributions, etc.…”