Hydrodynamic, conformational, and optical properties of cellulose tridecanoate molecules in solutions

Abstract

Cellulose tridecanoates of various molecular weights were synthesized, and their characteristics in chloroform and tetrachloroethane solutions were studied by methods of translational diffusion, velocity sedimentation, fl ow birefringence (Maxwell's method), and viscometry. The effects of solvent and temperature on the conformational characteristics of the macromolecules under consideration were examined. The anisotropy of the monomeric unit of cellulose tridecanoates was studied, and the contribution of pendant chains to the optical anisotropy of macromolecules of cellulose esters with aliphatic substituents was analyzed.Amphiphilic properties of aliphatically substituted cellulose in combination with high equilibrium rigidity of the molecules make it an attractive object for preparing mono-and multilayer LangmuirBlodgett nanofi lms. Successful use of such fi lms in micro-and nanoelectronics, analytical biotechnology, bioelectronics, and membrane technologies stimulates interest in studying the structure and conformational properties of the molecules of the starting compounds [1][2][3][4].In this work, we studied cellulose tridecanoate [CTD, pendant group CH 3 -(CH 2 ) 11 -CO-] by methods of molecular hydrodynamics and optics. We examined nine samples differing in the origin of the base (bacterial, wood, cotton, linter, microcrystalline cellulose) in chloroform (CF) and tetrachloroethane (TCE). The mean degree of substitution DS was 210. EXPERIMENTALThe intrinsic viscosity [η] was measured with an Ostwald capillary viscometer following the standard procedure [5]. In the measurements in CF, the temperature was varied in the interval 21-51°С. The diffusion coeffi cients D were measured with a polarization diffusometer [5] in a glass cell 3 cm long (along the beam) at 24°С. The solution concentration c did not exceed 0.1 × 10 -2 g cm -3 , which corresponded to practically limiting dilution. The fl otation coeffi cients -s 0 of CTD samples in chloroform (24°С) were determined with an analytical ultracentrifuge (МОМ, model 3180/В, Hungary) equipped with a polarization-interferometric attachment [5]. We used a layering two-sector cell with a polyamide insert. The rotor rotation rate was 40 × 10 3 rpm. The coeffi cients -s were extrapolated to zero concentration. The concentration was varied from 0.12 to 0.5 × 10 -2 g cm -3 . The molecular weights of the samples were determined from the measured diffusion (D) and fl otation (-s 0 ) coeffi cients by Svedberg's formula М sD = RТ(s 0 /D)(v -ρ 0 -1) -1 . The partial specifi c volume of the polymer is v -= 1.012 cm 3 g -1 . The refractive indices of the solutions and solvents were determined with a Mettler Toledo refractometer (model RM40, Switzerland) with an accuracy of 10 -4 ± 5 × 10 -5 .The intrinsic viscosities [η] (dl g -1 ) at 21°С, diffusion (D) and fl otation (-s 0 ) coeffi cients at 24°C, temperature