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Biological Stimulus-Responsive Hydrogels
Published in Severian Dumitriu, Valentin Popa, Polymeric Biomaterials, 2020
A.K. Bajpai, Sanjana Kankane, Raje Chouhan, Shilpi Goswami
Nugent et al. (McGann et al., 2009) developed novel pH-sensitive hydrogel composite for the delivery of aspirin to wounds using a freeze–thaw process. Physically cross-linked hydrogels composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) were prepared by a freeze–thaw treatment of aqueous solutions and aspirin was incorporated into the systems. The pH-sensitive nature of the hydrogels was apparent from solvent uptake studies carried out. Increasing alkaline media led to a greater degree of swelling due to increased ionization of PAA. The release rates shown by prepared hydrogels were relatively slow and exhibited non-Fickian release kinetics.
Moisture modeling and durability assessment of building envelopes
Published in Jan L.M. Hensen, Roberto Lamberts, Building Performance Simulation for Design and Operation, 2019
Aytaç Kubilay, Xiaohai Zhou, Dominique Derome, Jan Carmeliet
The main mechanism responsible for freeze-thaw damage to occur in porous building materials is phase change of water (Litvan 1988). In porous material, the volumetric expansion of water by 9% due to freezing exerts tensile stresses on the material matrix and causes damage when the stresses exceed the strength of the material matrix (Powers 1955; Everett 1961; Liso et al. 2007). One indicator, the number of freeze-thaw cycles, can be used to estimate the risk for freeze-thaw damage (Grossi et al. 2007). In this method, each freeze-thaw cycle is expected to add to the cumulative freeze-thaw damage similar to what occurs in mechanical fatigue with constant load cycles (Fagerlund 2000). Many studies often use, for simplicity, the number of zero crossings on a Celsius scale as the number of freeze-thaw cycles (Sedlbauer et al. 2000; Grossi et al. 2007; Klõšeiko et al. 2015; van Aarle et al. 2015). However, this approach fails to account for the fact that water in porous medium freezes at different temperatures below 0 °C, depending on the pore size.
Microbes from Cold Deserts and Their Applications in Mitigation of Cold Stress in Plants
Published in Ajar Nath Yadav, Ali Asghar Rastegari, Neelam Yadav, Microbiomes of Extreme Environments, 2021
Murat Dikilitas, Sema Karakas, Eray Simsek, Ajar Nath Yadav
Microorganisms thriving in harsh cold environments should have specific properties. They should produce AFPs, high levels of polyunsaturated fatty acids, ergosterol, proline, sugars, etc. Not only should these chemicals be produced in harsh conditions but also be renewed and topped up when they are consumed. The freeze-thaw cycle might deteriorate the physiological, biochemical and molecular functions. Under these circumstances, the antioxidant capacity and antimicrobial properties and even sporulation and mycelial developmental characteristics might be deteriorated (Dikilitas et al. 2011). Recently, Villarreal et al. (2018) reported that the yeasts Vishniacozymavictoriae, G. gastrica and Leucosporidium creatinivorum, isolated from Antarctica, were found to have cold-tolerant properties such as AFPs, fatty acids and ergosterol which could be used for industrial purposes. The North and South Poles represent the most inhospitable habitats in terms of cold and dry weather conditions, cold-adapted microorganisms in these regions could be important resources to study novel secondary metabolites and enzymes. There are quite a few microorganisms that have been successfully isolated and cultured from cold environments (Wang et al. 2017). These microorganisms have PGP properties, and could play vital roles in studies regarding plant-growth-promoting biocontrol, nitrogen fixation, antagonistic and alleviation of cold stress studies in plants. Although most of the recent studies conducted so far have largely focused on rhizobia, another interesting area that has come up recently concentrating on cold-active microorganisms that are also able to reduce the metal toxicity and harmful waste (Mishra et al. 2012).
Multiscale model for predicting freeze-thaw damage in asphalt mixtures
Published in International Journal of Pavement Engineering, 2022
Lisa Lövqvist, Romain Balieu, Nicole Kringos
Infiltration of moisture into the asphalt mixture by diffusion may lead to emulsification of the binder close to the surface (Varveri et al.2015) as well as stripping at the mastic-aggregate interface (Kringos et al.2008b). Additionally, in more open asphalt structures, the moisture might erode the asphalt as it flows through the air void system (Kringos et al.2008b). These mechanisms all cause a deterioration of material and structural properties that increase the risk of freeze-thaw damage, which occurs as the moisture trapped inside the air voids expands as it freezes to ice. The cyclic pressure inside the material caused by the freeze-thaw cycle may also lead to damage in the form of erosion, micro-cracks and chemo-mechanically induced deterioration of the material properties, eventually leading to an increase in volumetric pore volume in the mixture (Xu et al.2015). This effectively leads to an overall decrease of different properties of the mixture, such as its strength and stiffness (Feng et al.2010, Si et al.2014, Luo et al.2017, Pan et al.2017).
Recent advances in sludge dewatering and drying technology
Published in Drying Technology, 2022
Binqi Rao, Gongqin Wang, Peng Xu
The mechanism of microwave (MW) radiation includes thermal and non-thermal effects. The hydrogen bond is broken due to the alignment of the polarized part of the macromolecule with the pole of the electromagnetic field. The MW energy of water and organic compounds are characterized by constant polarization and induced polarization. It has been shown that MW pretreatment can release water originally bound to the particles, destroy the extracellular matrix, form a complex sludge polymer, change the structure of EPS, and increase the dissolution of microbial cell walls.[36] The experimental results of Rao et al.[25] show that microwave irradiation pretreatment can effectively improve the dewatering performance and reduce the MC of the sludge cake. When microwave power is less than the optimal microwave power, the MC decreases with the increase of the microwave time, and when it is greater than the optimal microwave power, the MC increases with the increase of microwave time. Freeze-thaw treatment is a method of freezing the sludge and thawing at room temperature to change the flocculation structure of the sludge and reduce the bound water.[37] Repeated freeze-thaw causes the crystalline expansion of the bound water in the cell and induces the cell to expand, which has a positive effect on removing the bound water in the cell.
Effect of liquid silane-based anti-stripping additives on rheological properties of asphalt binder and hot mix asphalt moisture sensitivity
Published in Road Materials and Pavement Design, 2020
Peyman Mirzababaei, Fereidoon Moghadas Nejad, Koorosh Naderi
The most common method to determine asphalt mixture moisture sensitivity is indirect tensile test (AASHTO T283). At least 6 asphalt samples were compacted by Marshall Hammer to obtain 7 ± 0.5 percent of air voids. Afterwards, the samples were divided into two categories: the first group was the control group, or “unconditioned” which were placed in a 25 ± 0.5°C water bath for 2 hours ± 10 minutes with a minimum of 25 mm of water above their surface, while the second group, or “conditioned”, was vacuum-saturated to 70-80 percent (AASHTO T283) with water and then placed in a freezer at -18 ± 3°C for 16 to 18 hours. It should be noted that the freeze/thaw cycles induce a new damage mechanism which is cracking from pore expansion. This mechanism can drastically increase the void content, as well as the connected void content within the mixture (Xu, Guo, & Tan, 2015). It may accelerate moisture damage and deteriorate ITS performance. The specimens were then placed in a 25 ± 0.5°C water bath for 2 hours ± 10 minutes with a minimum of 25 mm of water above their surface.