Hp Henk Huinink

Asymmetric block copolymers confined in a thin film

We have used a dynamic density functional theory (DDFT) for polymeric systems, to simulate the formation of micro phases in a melt of an asymmetric block copolymer, AnBm(fA=1/3), both in the bulk and in a thin film. In the DDFT model a polymer is represented as a chain of springs and beads. A spring mimics the stretching behavior of a chain fragment and the spring constant is calculated with the Gaussian chain approximation. Simulations were always started from a homogeneous system. We have mainly investigated the final morphology, adopted by the system. First, we have studied the bulk behavior. The diblock copolymer forms a hexagonal packed array of A-rich cylinders, embedded in a B-rich matrix. Film calculations have been done by confining a polymer melt in a slit. Both the slit width and surface-polymer interactions were varied. With the outcomes a phase diagram for confined films has been constructed. Various phases are predicted: parallel cylinders (C∥), perpendicular cylinders (C⊥), parallel lamella...

Morphology of symmetric block copolymer in a cylindrical pore

The influence of confinement on morphology formation in copolymer systems is an important area of interest in theoretical research. We apply dynamic density functional theory to investigate the effect of pores on the morphology formation in a symmetric diblock copolymer system. The pore is represented by a perfect cylindrical tube. Porous systems are important in biology and are gaining interest for applications in nanotechnology. We show that for the pore sizes under investigation two equilibrium morphologies are possible depending on the surface interaction: a perpendicular or slab morphology and a parallel or multiwall tube morphology. The latter is referred to in the article as dartboard morphology. In the dynamic pathway towards this morphology an intermediate metastable helical phase is found. An important observation is that, for a wide range of pore radii and variations of polymer chain length, no mixed parallel/perpendicular morphologies were found: All observed morphologies are insensitive to the pore diameter.

Ion transport and crystallization in inorganic building materials as studied by nuclear magnetic resonance

Salt weathering is a major cause of deterioration of buildings and monuments of cultural heritage. We have determined the underlaying moisture and ion transport within a representative building material by measuring the time evolution of NaCl-saturated samples during one-sided drying using nuclear magnetic resonance. The measured NaCl concentration profiles reflect the competition between advection to the surface and redistribution by diffusion. By representing the measured moisture and NaCl profiles in an efflorescence pathway diagram (EPD) the crystallization is also taken into account. The pathways followed in the EPD indicate that for historical objects in general, crystallization at the surface cannot be avoided.

How ions distribute in a drying porous medium: A simple model

Salt crystallization at surfaces is an important problem for buildings and monuments. We do not consider the formation of salt crystals as such, but focus on transport properties of ions in a drying porous medium. We deal with the first phase of the drying process, where the water is still uniformly distributed throughout the medium. An approximate model is presented, which accounts for both convection and diffusion. It is shown that the key parameter is the Peclet number at the evaporating surface, Pe≡hL/eD, where h, L, e, and D are the drying rate, sample size, porosity, and diffusion constant, respectively. When Pe≪1 (diffusion dominates over convection) the ions remain uniformly distributed throughout the system. Strong accumulation at the evaporating surface occurs for Pe≫1 (convection dominates over diffusion). Crossover behavior is found for Pe≈1. Therefore, it is likely that the first crystals will be formed both in the bulk and at the interfaces of the material when Pe≪1. For high values of Pe th...

Salt transport and crystallization in porous building materials.

Salt weathering is a major cause of deterioration of porous building materials. To obtain information about the mechanisms underlying these damage processes we have studied the moisture and ion transport. We measured the time evolution of NaCl saturated samples of fired-clay brick during one-sided drying using Nuclear Magnetic Resonance. The moisture content and amount of dissolved Na ions could be measured quantitatively as a function of position. The NaCl concentration profiles obtained from these data reflect the competition between advection to the surface and redistribution by diffusion. By representing the measured moisture and NaCl profiles in an efflorescence pathway diagram (EPD) also the crystallization can be taken into account.

One-dimensional scanning of moisture in heated porous building materials with NMR

In this paper we present a new dedicated NMR setup which is capable of measuring one-dimensional moisture profiles in heated porous materials. The setup, which is placed in the bore of a 1.5 T whole-body scanner, is capable of reaching temperatures up to 500 °C. Moisture and temperature profiles can be measured quasi simultaneously with a typical time resolution of 2-5 min. A methodology is introduced for correcting temperature effects on NMR measurements at these elevated temperatures. The corrections are based on the Curie law for paramagnetism and the observed temperature dependence of the relaxation mechanisms occurring in porous materials. Both these corrections are used to obtain a moisture content profile from the raw NMR signal profile. To illustrate the methodology, a one-sided heating experiment of concrete with a moisture content in equilibrium with 97% RH is presented. This kind of heating experiment is of particular interest in the research on fire spalling of concrete, since it directly reveals the moisture and heat transport occurring inside the concrete. The obtained moisture profiles reveal a moisture peak building up behind the boiling front, resulting in a saturated layer. To our knowledge the direct proof of the formation of a moisture peak and subsequent moisture clogging has not been reported before.

Dynamics of cross linking fronts in alkyd coatings

The dynamics of the curing process of alkyd coatings is an important aspect for coating performance. The formation of cross links in an alkyd coating film has been followed in time using a microimaging nuclear magnetic resonance setup, having a spatial resolution of 5μm perpendicular to the film. During this cross-linking process a front has been observed inside the coating film. The position of this front varied with the square root of time. With the help of a simple reaction model, we have proven that this dynamics results from the fact that the curing rate is limited by the oxygen flux into the coating. This model can also explain, the differences in curing rates observed for various coatings.

T2 distribution spectra obtained by continuum fitting method using a mixed Gaussian and exponential kernel function

Static (1)H NMR Free Induction Decay (FID) signals of polymer solids contain a lot of information about the molecular dynamics. A T2 analysis of the FID has generally been performed in terms of discrete two- or three-component models. However, this requires a priori assumption of the number of proton species before analysis. This paper presents a method of analyzing the FIDs of the polymer solid samples in terms of a continuous T2 distribution. A mixed Gaussian and Exponential kernel function was used to represent the true characteristic of FIDs of the polymer solids. A simple and realistic assumption has been made to reduce the number of degrees of freedom in the continuum fitting and to make the fitting stable. An experimental static (1)H NMR FID of a typical polymer solid sample was analyzed as an example in the end to demonstrate the application of this method.

Production of an Extracellular Matrix as an Isotropic Growth Phase of Penicillium rubens on Gypsum

ABSTRACT Indoor mold represents an important environmental concern, but a fundamental knowledge of fungal growth stages is needed to limit indoor fungal proliferation on finishing materials used in buildings. The present study focused on the succession of germination stages of the common indoor fungus Penicillium rubens on a gypsum substrate. This substrate is used as a model system representing porous materials that are widely used in indoor environments. Imaging with cryo-scanning electron microscopy showed that the formation of an extracellular matrix (ECM) is a phase of the isotropic growth of P. rubens that is uniquely related to germinating conidia. Furthermore, the ECM is observed only when a dry-state inoculation of the surface is applied, i.e., applying conidia directly from a 7-day-old colony, mimicking airborne contamination of the surface. When inoculation is done by spraying an aqueous conidial suspension, no ECM is observed. Moreover, it is concluded that the formation of an ECM requires active processes in the fungal cell. The porosity of the substrate proved that the ECM substance has high-viscosity characteristics. The present results stress that studies of indoor fungal growth should consider the method of inoculation, knowing that the common aqueous suspension may obscure specific stages in the initial phases of germination.

Bound and free water distribution in wood during water uptake and drying as measured by 1D magnetic resonance imaging

Knowledge on moisture transport in wood is important for understanding its utilization, durability and product quality. Moisture transport processes in wood can be studied by Nuclear Magnetic Resonance (NMR) imaging. By combining NMR imaging with relaxometry, the state of water within wood can be identified, i.e. water bound to the cell wall, and free water in the cell lumen/vessel. This paper presents how the transport of water can be monitored and quantified in terms of bound and free water during water uptake and drying. Three types of wood from softwood to hardwood were selected covering a range of low to high density wood; pine sapwood and oak and teak. A calibration is performed to determine the different water states in each different wood type and to convert the NMR signal into moisture content. For all wood types, water transport appeared to be internally limited during both uptake and drying. In case of water uptake, free water was observed only after the cell walls were saturated with bound water. In case of drying, the loss of bound water starts only after vanishing of free water, irrespective of the position. Obviously, there is always a local thermodynamic equilibrium of bound and free water for both uptake and drying. Finally, we determined the effective diffusion coefficient (Deff). Experimentally determined diffusion constants were compared with those derived by the diffusion models for conceptual understanding of transport mechanism. We found that diffusion in the cell wall fibers plays a critical role in the transport process.