Abstract
The structure and mechanical properties of model polymer networks consisting of alternating tetra-functional poly(ethylene glycol)s (PEGs) and bis-functional linear PEGs were investigated by dynamic light scattering and rheological measurements. The sizes of the correlation blob () and the elastic blob () were obtained from these measurements and compared to the theoretical mesh size, the geometric blob (), calculated by using the tree-like approximation. By fixing the concentration of tetra-PEGs and tuning the molecular weight of linear-PEGs, we systematically compared these blob sizes in two cases: complete network (Case A) and incomplete network (Case B). The correlation blob, , obtained by dynamic light scattering (DLS) was found to obey the well-known concentration dependence for polymer solutions in semidilute regime () irrespective of the Cases. On the other hand, the was strongly dependent on the Cases: For Case A, was weakly dependent on the molecular weight of linear-PEGs () while for Case B was a strong increasing function of (). However, both of them are different from the geometric blob (theoretical mesh) of the gel networks. In addition, interesting relationships between and , , , were obtained for Cases A and B, respectively.
Highlights
The mesh size is an ambiguous characteristic length in polymer gels
Many different sizes have been used as mesh size, including correlation blob (ξ c ) by scattering experiments [3,4], elastic blob (ξ el ) by rheological measurements [3,5], and mesh-like structure observed in scanning transmittance electron microscopes (STEM) [6,7]
The geometric blob, the correlation blob, and the elastic blob are the elastic blob are estimated from theoretical calculation, dynamic light scattering (DLS) and rheological measurements, respectively, and their physical meaning are discussed in detail
Summary
The mesh size is an ambiguous characteristic length in polymer gels. The most intuitive mesh size in a gel for most readers is probably the distance between crosslinkers. Tetra-PEG-A (red) and -B (blue) macromers are crosslinked alternatively, forming a threeinfinite polymer network. The elastic The modulus tetra-PEGs is well-described by the phantom dimensional infinite polymer network. Zernike (0)/(1 + of ),φ irrespective as farconcentration as the polymerisconcentration is in concentration regime [18] This means that the structures of tetra-PEG gels are the same as that of the semidilute concentration regime [18]. Has beenand believed that the equi-molecular networks consisting of tetra-PEGs with equi-molecularIt weights equi-functionality. It has been weight and equi-functionality are the necessary conditions for preparation of “ideal”.
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