Effects of carbon nanotubes on rheological behavior in cellulose solution dissolved at low temperature

Investigation of Cellulose-Based Materials Applied in Life Sciences Using Laser Light Scattering Methods

This review emphasizes the practical importance of laser light scattering methods for characterizing cellulose and its derivatives. The physicochemical parameters like molecular weights, the radius of gyration, hydrodynamic radius, and conformation will be considered when the reproducibility of polymer behavior in solution is necessary for the subsequent optimization of the property profile of a designed product. Since there are various sources of cellulose, and the methods of cellulose extraction and chemical modification have variable yields, materials with variable molecular weights, and size polydispersity will often result. Later, the molecular masses will influence other physicochemical properties of cellulosic materials, both in solution and solid state. Consequently, the most rigorous determination of these quantities is imperative. In this regard, the following are presented and discussed in this review: the theoretical foundations of the light scattering phenomenon, the evolution of the specific instrumentation and detectors, the development of the detector-coupling techniques which include a light scattering detector, and finally, the importance of the specific parameters of polymers in solution, resulting from the data analysis of light scattering signals. All these aspects are summarized according to the chemical classification of the materials: celluloses, esters of cellulose, co-esters of cellulose, alkyl esters of cellulose, ethers of cellulose, and other heterogeneous cellulose derivatives with applications in life sciences.

Concentration-independent mechanics and structure of hagfish slime

The defense mechanism of hagfish slime is remarkable considering that hagfish cannot control the concentration of the resulting gel directly; they simply exude a concentrated material into a comparably "infinite" sea of water to form a dilute, sticky, cohesive elastic gel. This raises questions about the robustness of gel formation and rheological properties across a range of concentrations, which we study here for the first time. Across a nearly 100-fold change in concentration, we discover that the gel has similar viscoelastic time-dependent properties with constant power-law exponent (α=0.18±0.01), constant relative damping tanδ=G^''/G^'≈0.2-0.3, and varying overall stiffness that scales linearly with the concentration (∼c^0.99±0.05). The power-law viscoelasticity (fit by a fractional Kelvin-Voigt model) is persistent at all concentrations with nearly constant fractal dimension. This is unlike other materials and suggests that the underlying material structure of slime remains self-similar irrespective of concentration. This interpretation is consistent with our microscopy studies of the fiber network. We derive a structure-rheology model to test the hypothesis that the origins of ultra-soft elasticity are based on bending of the fibers. The model predictions show an excellent agreement with the experiments. Our findings illustrate the unusual and robust properties of slime which may be vital in its physiological use and provide inspiration for the design of new engineered materials.

STATEMENT OF SIGNIFICANCE

Hagfish produce a unique gel-like material to defend themselves against predator attacks. The successful use of the defense gel is remarkable considering that hagfish cannot control the concentration of the resulting gel directly; they simply exude a small quantity of biomaterial which then expands by a factor of 10,000 (by volume) into an "infinite" sea of water. This raises questions about the robustness of gel formation and properties across a range of concentrations. This study provides the first ever understanding of the mechanics of hagfish slime over a very wide range of concentration. We discover that some viscoelastic properties of slime are remarkably constant regardless of its concentration. Such a characteristic is uncommon in most known materials.

Mechanical, dielectric, and rheological properties of poly(arylene ether nitrile)–reinforced poly(vinylidene fluoride)

In this study, poly(vinylidene fluoride) (PVDF) and poly(arylene ether nitrile) (PEN) polymer alloys with different mass ratios were prepared by solution casting method. The morphological, thermal, dielectric, mechanical, and rheological properties of the obtained polymer alloys were systematically studied. Scanning electron microscopic images showed that the polymer alloys exhibited two-phase system with PEN dispersed in PVDF matrix, which was consistent with the Cole–Cole plots obtained from rheological study. With the introduction of PEN, the crystallinity of the alloys decreased obviously, the dielectric properties of the alloys were stable before the melting temperature. When the content of PEN increased to 7 wt%, both the tensile strength and elastic modulus reached the maximum values (35.1 MPa and 1545.3 MPa), with an increment of 24% and 31% compared with those of PVDF, respectively. Rheological studies showed that the addition of PEN could obviously broaden the linear viscoelastic region of PVDF. Furthermore, the complex viscosities and storage modulus of polymer alloys increased obviously with the addition of PEN.

MWCNT-reinforced polyarylene ether nitrile nanocomposites

In this study, we investigated the effect of surface roughness of acidulated multi-walled carbon nanotube (MWCNT) on the physical performances of MWCNT/polyarylene ether nitrile (MWCNT/PEN) nanocomposites. Acidulated MWCNTs with different surface roughnesses were prepared by ultrasonicating and refluxing of MWCNTs in the mixture solvent of sulfuric acid/nitric acid and characterized by atomic force microscopy. With longer acidulating time, more and more oxygen functional groups including carboxyl and hydroxyl groups which result in the coarser surface of the obtained MWCNT, were generated. MWCNT/PEN composites were fabricated by using the solution-casting method with the acidulated MWCNTs and PEN. SEM observation showed that the acidulated MWCNTs are well-embedded in the polymer matrix without aggregation. differential scanning calorimetry and thermogravimetric analysis results showed that the incorporation of acidulated MWCNTs can improve the thermal behavior of the resulted polymer composites. The coarser the surface of the acidulated MWCNT, the better the mechanical performances of the obtained composites, while opposite results were observed for the dielectric properties of the nanocomposites. The dynamical rheological results showed that a better compatibility between the MWCNT and PEN is achieved when the coarser MWCNT is used.

Rheology, morphology, and properties of polyarylene ether nitrile blends

Polyarylene ether nitrile (PEN) blends with different mass ratios of PEN bisphenol (BP) to PEN bisphenol A (BPA) were prepared by solution casting method. The morphological, rheological, thermal, dielectric, and mechanical properties of the resulted blends were systematically studied. Rheological studies show that the addition of PEN (BPA) could improve the flowability of blends except that of 90/10 (BP/BPA). Meanwhile, the crystallization degree of blends also decreases except that of 90/10 (BP/BPA). Mechanical measurement results indicate that the PEN blend (PEN (BP):PEN (BPA) of 90:10) possesses highest tensile strength of 119.7 MPa, increased by 28.6% than PEN blends (PEN(BP):PEN(BPA) of 50:50). Besides, the scanning electron microscopic images show that there exists phase separation in the PEN blends (PEN (BP):PEN (BPA) of 50:50), which is well consistent with the Cole–Cole plots obtained from rheological studies. Moreover, the phenomenon of phase separation will lead to interfacial polarization between the two different phases, which is a significant factor to induce the transformation of dielectric constant. Furthermore, all blends possess high thermal stability (initial decomposition temperature over 470°C) and high mechanical property (tensile strength over 93 MPa), suggesting that PEN blends (BP/BPA) have a good prospect of extension and application.