Moisture in Textiles

The interactions of textiles with moisture have been thoroughly studied in textile research, while fluid mechanists and soft matter physicists have partially investigated the underlying physics phenomena. A description of liquid morphologies in fibrous assemblies allows one to characterize the associated capillary forces and their impact on textiles, and to organize their complex moisture transport dynamics. This review gathers some of the common features and fundamental mechanisms at play in textile–liquid interactions, with selected examples ranging from knitted fabrics to nonwoven paper sheets, associated with experiments on model systems. Expected final online publication date for the Annual Review of Fluid Mechanics, Volume 54 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Comprehensive multidimensional study of the self-assembly properties of a three residue substituted β3 oligoamide

Substituted β3 oligoamides form a unique self-assembling system where each monomer folds into a helix containing approximately three β3 amino acids per turn, yielding a geometrically well-defined cylindrical building block that, when N-acylated, is able to self-assemble head-to-tail into nanorods that can reach several 100 μm length. It was shown in previous works that self-assembly can be achieved with a three residue long oligoamide as well that lacks any intramolecular H-bonds, yet it crystallizes in a helix-like conformation. The self-assembly properties of these small oligoamides are however elusive, suggesting a more complex system than the self-assembly of the H-bond stabilized helical monomers. Here we focus on the self-assembly behaviour of a three residue oligoamide, Ac-β3[LIA] where the letters denote the side chain of the analogous α amino acid. Ac-β3[LIA] can yield highly inhomogeneous suspensions in water with a broad range of large fibrous structures that seem to be very stable, yet occasionally fibre growth is only observed upon heating. The small size of the monomer suggests a highly dynamic equilibrium yet all previous attempts failed to clearly identify low molecular weight species. Therefore a special methodology was employed in this study to characterize the suspensions at different size ranges: SANS that is optimal to measure the small oligomers and cross sectional diameter of the assemblies, DLS that is sensitive to the large populations and therefore the length of the superstructures, and NMR that is sensitive to monomeric and small oligomeric form, in conjunction with IR spectroscopy to probe the folding and AFM to image the morphology of the assemblies. Temperature ramping was used to perturb the system to probe the dynamicity of the self-assembly. It was found that the anomalous self-assembly behaviour of Ac-β3[LIA] is caused by its two stable conformations, a helix-building “horseshoe” fold and a linear conformer. The latter is exclusively found in monomeric form in solution whereas the horseshoe fold is stable in solid phase and in fibrous assemblies. Small oligomers were absent. Thus the self-assembly of Ac-β3[LIA] is arrested by the activation energy need of the conformation change; fibre growth might be triggered by conditions that allow increased conformational freedom of the monomers. This observation may be used to develop strategies for controlled switchable self-assembly.

Sound absorption of gradient structure fabrics based on functional finishing with metal compounds

The common porous sound absorbing materials are thick and have a narrow sound absorption band. In order to design light and thin gradient structure functional fibrous assemblies with excellent performance of sound absorption and noise reduction, metal compounds with a heavy vibration damping characteristic were applied to a nonwoven by padding finishing, dipping finishing (DF) and spraying finishing. The influences of metal compound type, finishing method, the application amount of finishing agent and distribution of the finishing agent on nonwoven fabric for the sound absorption performance were studied. The results showed that the samples following DF had the largest amount of metal compound applied, and this processing method was beneficial to the construction of the gradient structure. The heavy vibration damping property of the metal compound could combine with the porous sound absorption mechanism of the nonwoven fabric to improve the sound absorption performance of fabric. The greater the amount of metal compound in the application, the better the sound absorption performance, and the effects of ferric oxide (Fe2O3) and barium sulfate (BaSO4) were particularly remarkable. Different finishing methods would affect the distribution of the metal compound on the material, which in turn affected the sound absorption performance.

Evaluating compressive behavior of general fibrous assemblies

General fibrous assemblies are made of loose fibers and air filling in the pores formed by these fibers. An important characteristic of these assemblies is their mechanical behavior under compression and release. In this paper, a unified and systematic experimental investigation was used to quantify and characterize the compressional and recovery behavior of several randomly oriented fibrous assemblies via mechanical and conductive in situ integrated measurement system. An attempt was made to characterize the curves of force, modulus, work and energy loss during compressional and recovery cycles. Considerable hysteresis occurred between the compression and release operations which is an evidence for the existence of fiber slippage and frictional effects. Work, energy loss and recovery rate of work turned out to have a nonlinear exponential relationship with cycles.

Estimation of fiber orientation and length distribution in cashmere fibrous assemblies

In a general fibrous assembly, single fiber orientation as well as fiber length distributions are important characteristics because they directly influence the properties of textiles. An X-ray micro-tomography experiment with a high resolution of 3 μm was for the first time conducted on a randomly oriented inner Mongolia cashmere fibrous assembly to get a series of two-dimensional projections from different angles and the corresponding cone–beam algorithm proposed by Feldkamp and volume rendering technique were used to realize the three-dimensional (3D) reconstruction. An automated segmentation algorithm described by Rigort and Weber was used to trace and detect single fibers from tomographic 3D data. Local normalized cross-correlation of the tomograms was computed with a cylindrical template that mimics a short microtubule segment to get two new objects, named the correlation and orientation fields. Tracing results of fiber length and orientation distributions were given in this paper statistically.