Dynamic mechanical relaxation of cross-linked styrene-butadiene polymers containing free chains: Possibility of reptation

The structure of styrene-butadiene rubbers (SBRs) consists of chains attached to cross-links of relatively small number density. These rubbers show an α-relaxation process that is attributed to segmental motions of the attached chains. To investigate how an SBR's rubber-like behavior would change when free chains interpenetrate its structure, we prepared one SBR of mol wt 120 × 10³ containing 3–4% free chains of identical mol wt, and studied its dynamic mechanical relaxation. For 0.1 Hz frequency measurements, the α-relaxation peak appeared at 210 K, and a second relaxation peak, which we refer to as α_R-relaxation, at 300 K. A third relaxation of small magnitude was resolved at temperatures between the α_R- and the α-relaxation peaks, and its origin was discussed in relation to other studies. Spectral features of the α_R-and the α-relaxations were found similar. We investigated the merits of the time-temperature superposition of the α- and of the α_R-relaxations. The α_R relaxation vanished when the free chains were extracted from the SBR by swelling-extraction procedure. The features of α-relaxation can be interpreted as segmental motions of the SBR, but the features of the α_R-relaxation is be interpretable only in terms of tube model for diffusion of free chains in a lightly cross-linked structure. We estimated the mol wt of these free chains and the mass between entanglements, and then used these quantities to calculate, by using the Doi-Edwards formalism, the relaxation time of the α_R-process at 293 K. This relaxation time agrees with the experimental value. The α_R-relaxation seems consistent with the tube model for diffusion of free chains in the cross-linked structure of SBR.     

The exposure of a fresh fruit and vegetable supply chain to global water-related risks

ABSTRACT

We have combined estimates of the UK’s supply of fresh fruit and vegetables (1996 – 2015) with estimates of water requirements and water scarcity in producing countries, to identify where the supply is exposed to physical, regulatory and reputational water risks and how this has changed over time. Some 76% of the freshwater consumed in the supply of fresh fruit and vegetables to the UK is withdrawn overseas. The supply chain is particularly exposed to water risks in Spain, Egypt, South Africa, Chile, Morocco, Israel and Peru. Exposure has increased over time.     

The experiences in close relationships—Relationship Structures Questionnaire: A method for assessing attachment orientations across relationships.

Most research on adult attachment is based on the assumption that working models are relatively general and trait-like. Recent research, however, suggests that people develop attachment representations that are relationship-specific, leading people to hold distinct working models in different relationships. The authors report a measure, the Relationship Structures questionnaire of the Experiences in Close Relationships—Revised (ECR-RS; R. C. Fraley, N. G. Waller, & K. A. Brennan, 2000), that is designed to assess attachment dimensions in multiple contexts. Based on a sample of over 21,000 individuals studied online, it is shown that ECR-RS scores are reliable and have a structure similar to those produced by other measures. In Study 2 (N = 388), it is shown that relationship-specific measures of attachment generally predict intra- and interpersonal outcomes better than broader attachment measures but that broader measures predict personality traits better than relationship-specific measures. Moreover, it is demonstrated that differentiation in working models is not related to psychological outcomes independently of mean levels of security. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

陶瓷-熔融盐复合相变储能材料（英文）CSCD

研究了石墨材料包括纳米石墨对基于硝酸盐陶瓷复合相变储热材料性能的影响。其目的在于制备一种可用于集中式太阳能热发电(CSP)和工业废热回收(IWH)等应用的新型高温复合相变材料,并且使用导热增强物质(TCE)提升相变材料的导热性能。复合相变储热材料主要由硝酸钠(NaNO_3)相变材料,氧化镁(MgO)陶瓷基体,以及不同种类、不同比例的石墨导热增强剂组成。通过对复合材料的形态及热物理性质测定表明:不同种类的石墨导热增强剂对复合材料的导热性能影响不同,复合材料的储热密度随复合材料中相变材料比例的增加而增加。所得基于硝酸盐的陶瓷复合材料均可在500℃保持良好的热稳定性,因此其潜在应用包括工业废热回收及集中式太阳能热发电系统(CSP)等。     

Phase Transitions from Incoherent and from Coherent Metal Phases in Quasi-One-Dimensional Organic Conductors

We study effects of a preformed Mott gap and dimensionality on interchain one-particle coherence and spin-density-wave phase transitions in weakly-coupled dimerized quarter-filled Hubbard chains. A phase diagram is given, based on the two-loop perturbative renormalization-group (RG) approach together with the random phase approximation. Feedback effects of interchain processes on the umklapp process are examined by the 1 + expansion. We discuss relevance of the present result to the SDW phase transitions in the quasi-one-dimensional dimerized quarter-filled organic conductors, (TMTTF) ₂ X and (TMTSF) ₂ X.