DataSheet1_Constraining effects on polymer chain relaxation in crosslinked supramolecular dual networks.docx

Polymer networks containing transient physical and permanent chemical cross-links exhibit unique mechanical properties due to the intrinsic reassociating ability of supramolecular functional groups. Similar to supramolecular gels, these networks allow the controlled release of stored energy and can extend the life of polymer networks in practical applications. In this study, we investigated the rheology, dielectric spectroscopy, stress–strain behavior, and dynamic mechanical analysis of networks based on long polybutylene oxide (PBO) chains functionalized with randomly placed thymine (Thy) side groups. A transient network was formed by proportionally mixing this matrix with short non-entangled linear 1,3,5-diaminotriazine (DAT) head–tail modified PBO chains, exploiting the hetero-complementarity of the DAT–Thy triple hydrogen bond. This transient polymer network was further cross-linked to a dual network via a thiol-ene click reaction to form static covalent bonds. In PBO, the similar polarity of the PBO matrix and the DAT–Thy functional groups ensures that the molecular chain motion is not affected by segregation, resulting in a homogeneous polymer phase without microphase-separated functional group domains. Dielectric relaxation spectroscopy was combined with rheology to quantify the relaxation processes of the interconnected polymers and the strength of the DAT–Thy bonding interactions in the melt. The results showed two distinct plateaux in the relaxation modulus due to contributions from hydrogen and permanent bonds. In the case of the dual network, the lifetime of the hydrogen bond was prolonged and higher activation energy was observed due to the physical cross-link preventing the movement of the long chain.</p

Effects of Core Microstructure on Structure and Dynamics of Star Polymer Melts: From Polymeric to Colloidal Response

The structure and linear viscoelastic behavior of four different model star polymer melts were investigated experimentally. The star polymers were prepared via different synthetic routes based on atom transfer radical polymerization (ATRP). Stars with small elongated (linear backbone) cores exhibited slight differences in the asymmetry of the core, which however did not affect the rheological properties significantly. The relaxation behavior of these stars with an asymmetric core was well-described by available tube models. On the other hand, stars with large cross-linked cores exhibited a core–shell morphology and their stress relaxation was dominated by a power-law decay over about 8 decades, akin to gel-like soft systems. This behavior reflected their liquid-like ordering and small intercore distances, and bares analogueies to that of interpenetrating soft colloids and microgels

The equilibrium shear module of silicone elastomers is controlled by the concentration of hydrosilane c_Si-H.

<p>Data for PDMS elastomers: Squares, black: system 1, at a catalyst concentration of 0.5 ppm (solid symbols) and less (open symbols); Crosses: system 2; Squares, red: system 3; Dashed line is an empirical fit, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195180#pone.0195180.e007" target="_blank">Eq 7</a>, cf. text. Numerical values can be found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195180#pone.0195180.s017" target="_blank">S11 Dataset</a>.</p

Chemically defined, ultrasoft PDMS elastomers with selectable elasticity for mechanobiology

<div><p>Living animal cells are strongly influenced by the mechanical properties of their environment. To model physiological conditions ultrasoft cell culture substrates, in some instances with elasticity (Young's modulus) of only 1 kPa, are mandatory. Due to their long shelf life PDMS-based elastomers are a popular choice. However, uncertainty about additives in commercial formulations and difficulties to reach very soft materials limit their use. Here, we produced silicone elastomers from few, chemically defined and commercially available substances. Elastomers exhibited elasticities in the range from 1 kPa to 55 kPa. In detail, a high molecular weight (155 kg/mol), vinyl-terminated linear silicone was crosslinked with a multifunctional (f = 51) crosslinker (a copolymer of dimethyl siloxane and hydrosilane) by a platinum catalyst. The following different strategies towards ultrasoft materials were explored: sparse crosslinking, swelling with inert silicone polymers, and, finally, deliberate introduction of dangling ends into the network (inhibition). Rheological experiments with very low frequencies led to precise viscoelastic characterizations. All strategies enabled tuning of stiffness with the lowest stiffness of ~1 kPa reached by inhibition. This system was also most practical to use. Biocompatibility of materials was tested using primary cortical neurons from rats. Even after several days of cultivation no adverse effects were found.</p></div

Dependence of sol fraction on stoichiometric ratio.

<p>Dependence of sol fraction on stoichiometric ratio.</p

Change of rheological properties due to addition of inert filler polymers.

<p>Frequency dependence of the storage (G', solid symbols) and loss modules (G", open symbols) at a strain of 1%. All samples: r = 0.71 and 0.5 ppm catalyst; Squares: neat system; Circles: 25% (v/v) of 139 kg/mol inert PDMS added; Triangles: 25% (v/v) of 68 kg/mol inert PDMS added; Diamonds: 25% (v/v) of 28 kg/mol inert PDMS added. Raw data can be found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195180#pone.0195180.s013" target="_blank">S7 Dataset</a>.</p

The stoichiometric ratio controls viscoelastic response.

<p>Frequency dependence of storage (G', solid symbols) and loss modules (G", open symbols); squares stoichiometric ratio r = 1.28; circles: r = 1.00; triangles: r = 0.71. Red line: power law expected for a critical gel (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195180#sec017" target="_blank">discussion</a>). Raw data can be found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195180#pone.0195180.s010" target="_blank">S4 Dataset</a>.</p

Inhibition results in ultrasoft elastomers.

<p>Frequency dependence of the storage (G', solid symbols) and loss modules (G", open symbols). All measurements 1% strain and stoichiometric ratio 1.28. Squares: 0.5 ppm catalyst and c_inhibitor = 0% (neat system); Circles: 0.5 ppm catalyst and w_inhibitor = 0.25%; Triangles: 1.0 ppm catalyst and c_inhibitor = 2%. Raw data can be found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195180#pone.0195180.s014" target="_blank">S8 Dataset</a>.</p

The loss factor tan δ = G''/G' is independent of filler molecular weight.

<p>All samples stoichiometric ratio 0.71 and 0.5 ppm catalyst. Squares: Neat elastomer (system 1); all other systems 25% inert silicone polymer added with molecular weights of 28 kg/mol (circles), 68 kg/mol (up triangles), and 139 kg/mol (down triangles), respectively. Raw data can be found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195180#pone.0195180.s016" target="_blank">S10 Dataset</a>.</p

The loss module may be approximated by power laws in some regions.

<p>The local slope of G'' in a double logarithmic plot, i.e. the effective exponent n, as a function of angular frequency; (triangles) elastomer with r = 1.21; (squares) r = 0.84; (stars) r = 0.71. Raw data can be found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195180#pone.0195180.s011" target="_blank">S5 Dataset</a>.</p