Multidimensional Vascularized Polymers using Degradable Sacrificial Templates

Complex multidimensional vascular polymers are created, enabled by sacrificial template materials of 0D to 3D. Sacrificial material consisting of the commodity biopolymer poly(lactic acid) is treated with a tin catalyst to accelerate thermal depolymerization, and formed into sacrificial templates across multiple dimensions and spanning several orders of magnitude in scale: spheres (0D), fibers (1D), sheets (2D), and 3D printed. Templates are embedded in a thermosetting polymer and removed using a thermal treatment process, vaporization of sacrificial components (VaSC), leaving behind an inverse replica. The effectiveness of VaSC is verified both ex situ and in situ, and the resulting structures are validated via flow rate testing. The VaSC platform is expanded to create vascular and porous architectures across a wide range of size and geometry, allowing engineering applications to take advantage of vascular designs optimized by biology.     

The finite volume method approach to the collapsed dimension method in analyzing steady/transient radiative transfer problems in participating media

With the finite volume formulation (FVM) approach applied to the collapsed dimension method (CDM), this article deals with the application of the CDM to analyze radiative heat transfer problems in a participating medium subjected to a continuous diffuse or a continuous/short-pulse collimated boundary radiative loading. The planar medium contained between diffuse gray boundaries is absorbing, emitting and anisotropically scattering. With three categories of thermal boundary radiative loadings, for the four types of problems considered, the CDM results are compared for a wide range of radiative parameters with that of the FVM.     

Modeling of combustion and ignition of solid-propellant ingredients

Techniques for modeling energetic-material combustion and ignition have evolved tremendously in the last two decades and have been successfully applied to various solid-propellant ingredients. There has been a paradigm shift in the predictive capability of solid-propellant combustion models as the field has advanced from a simple and global-kinetics approach to a detailed approach that employs elementary reaction mechanisms in the gas phase, and accommodates thermal decomposition and subsequent reactions in the condensed phase. The detailed models not only allow calculation of propellant burning-rate characteristics, such as pressure and temperature sensitivities, but also of the surface conditions and entire combustion-wave structure, including the spatial variations in temperature and species concentrations.

This paper provides a comprehensive review of recent advances in the modeling and simulation of various solid-propellant ingredients over a wide range of ambient conditions. The specific materials of concern include nitramines (RDX, HMX), azides (GAP), nitrate esters (NG, BTTN, TMETN), ADN, and AP monopropellants, as well as homogeneous mixtures representing binary (RDX/GAP, HMX/GAP, and AP/HTPB) and ternary (RDX/GAP/BTTN) pseudo-propellants. Emphasis is placed on the steady-state combustion and laser-induced ignition of nitramines. The capabilities and deficiencies of existing approaches are addressed. In general, the detailed gas-phase reaction mechanisms developed so far represent the chemistry of monopropellants and associated mixtures consistently well, and help understand the intricate processes of solid-propellant combustion. The reaction mechanisms in the condensed phase, however, still pose an important challenge. Furthermore, the current knowledge of the initial decomposition of molecules emerging from the propellant surface is insufficient to render the models fully predictive. Modeling is thus not yet a predictive tool, but it is a useful guide. In the near future, it is likely that detailed combustion models can assist in the formulation of advanced solid propellants meeting various performance and emission requirements.     

Analysis of conduction-radiation problem in absorbing, emitting and anisotropically scattering media using the collapsed dimension method

Combined conduction-radiation problem is solved using the collapsed dimension method. One-dimensional gray planar absorbing, emitting and anisotropically scattering medium is considered. Non-dimensional medium temperature and heat flux distributions are found for various values of boundary temperature, optical thickness, boundary emissivity and conduction-radiation parameter. Effects of scattering albedo and anisotropy factor are also discussed. For comparison, problems considered are also analyzed with the discrete transfer method and the exact method. Collapsed dimension method is found to give excellent comparison for various radiative parameters considered.     

Graphene oxide/ferrofluid/cement composites for electromagnetic interference shielding application

This paper deals with the preparation of graphene oxide-ferrofluid-cement nanocomposites to evaluate the electromagnetic interference (EMI) shielding effectiveness (SE) in the 8.2-12.4 GHz frequency range. It has been observed that incorporation of graphene oxide (30 wt%) along with an appropriate amount of ferrofluid in the cement matrix leads to a shielding effectiveness of 46 dB (>99% attenuation).The presence of graphene oxide and ferrofluid in the cement leads to strong polarizations and magnetic losses that consequently result in higher shielding effectiveness compared to pristine cement. The resulting nanocomposites have shown Shore hardness of 54 and dc conductivity of 10.40 S cm( - 1). SEM reveals the homogeneous dispersion of graphene oxide and ferrofluid in the cement matrix.     

Effects of gellant concentration on the burning and flame structure of organic gel propellant droplets

The increasing demand for higher energy density fuels and the ever-increasing concern for their safety have propelled research in the field of gel propellants. For studying the fundamental parameters without the interference of neighbouring droplets, an isolated droplet was chosen to investigate experimentally the combustion process of gel propellants under normal gravity conditions. Phase separation of the gel propellant components leading to bubble nucleation, vapor jetting and microexplosions were found to be the main phenomenon involved during the combustion period. Experiments were comprehensively carried out to study the effect of gellant concentration on the burning rate constant as well as flame structure. The burning rate constant was found to decrease with increase in the gellant concentration. Decrease in the calorific value of the increasing gellant concentrations was proposed as one of the reasons for this variation. The flame exhibited a triple flame structure for all the cases for both radicals as well luminous flames. The horizontal and vertical flame standoff distances were observed to decrease with gellant content. Decrease in the content of the base fuel was proposed as the reason for the same.     

Long-term and fast-bactericidal activity of methacrylamide-based copolymer for antibiofilm coatings and antibacterial wipes applications

Bacterial-related infections can be hazardous for human health and the surrounding environment. Traditional antibiotic-based treatments for these infections are increasingly ineffective due to the emergence of antibiotic-resistant bacteria. Antimicrobial peptide mimics have emerged as promising replacements owing to their potency against bacteria and lack of susceptibility to generate resistant cells. Thus, we synthesized a random copolymer, consisting of aminopropyl methacrylamide and benzyl methacrylamide (AB polymer) by random co-polymerization that mimics host–defense antimicrobial peptides. For its use as a coating, the AB polymer is drop-casted onto a cleaned glass substrate and tested for its antibacterial activity toward Escherichia coli and Staphylococcus aureus, wherein almost 99% of antibacterial activity was observed within 5 min. The prepared coating also possessed excellent longevity characteristics of up to 5 weeks. The AB polymer is also able to inhibit biofilm formation as well as disrupt a mature biofilm and can also be employed as an antibacterial wipe for cleaning bacterial contaminated surfaces. Mechanism study through SEM analysis showed that the AB polymer ruptures the bilayer membrane of both bacterial strains, thereby leading to pore formation causing cell death. Cell viability study depicted that 71% of the A549 lung carcinoma epithelial cells are viable compared to 80% on bare glass substrate. Thus, the synthesized AB polymer may be used in a variety of antibacterial applications directly in the form of solution (wipes) or forming a coating (drop casted/spray coated) for battling bacterial colonization.