Surface Measurement Systems LTD

Middlesex, United States

Surface Measurement Systems LTD

Middlesex, United States
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Smith R.R.,Imperial College London | Shah U.V.,Imperial College London | Parambil J.V.,Imperial College London | Burnett D.J.,Surface Measurement Systems Ltd. | And 2 more authors.
AAPS Journal | Year: 2017

The aim of this work was to assess the effect of different crystalline polymorphism on surface energetics of D-mannitol using finite dilution inverse gas chromatography (FD-IGC). Pure α, β and δ polymorphs were prepared via solution crystallisation and characterised by powder X-ray diffraction (P-XRD). The dispersive surface energies were found to range from 43 to 34 mJ/m2, 50 to 41 mJ/m2, and 48 to 38 mJ/m2 , for α, β, and δ, respectively, for surface coverage ranging from 0.006 to 0.095. A deconvolution modelling approach was employed to establish their energy sites. The primary sites corresponded to maxima in the dispersive surface energy of 37.1 and 33.5; 43.3 and 39.5; and 38.6, 38.4 and 33.0; for α, β, and δ, respectively. This methodology was also extended to an α-β polymorph mixture to estimate the amount of the constituent α and β components present in the sample. The dispersive surface energies of the α-β mixture were found to be in the range of 48 to 37 mJ/m2 with 40.0, 42.4, 38.4 and 33.1 mJ/m2 sites. The deconvolution modelling method extracted the energy contribution of each of the polymorphs from data for the polymorphic mixture. The mixture was found to have a β-polymorph surface content of ∼19%. This work shows the influence of polymorphism on surface energetics and demonstrates that FD-IGC coupled with a simple modelling approach to be a powerful tool for assessing the specific nature of this energetic distribution including the quantification of polymorphic content on the surface. © 2016, American Association of Pharmaceutical Scientists.


Brum J.,Glaxosmithkline | Burnett D.,Surface Measurement Systems Ltd.
AAPS PharmSciTech | Year: 2011

We investigate the use of dispersive surface energy in quantifying surface amorphous content, and the concept of effective amorphous surface area is introduced. An equation is introduced employing the linear combination of surface area normalized square root dispersive surface energy terms. This equation is effective in generating calibration curves when crystalline and amorphous references are used. Inverse gas chromatography is used to generate dispersive surface energy values. Two systems are investigated, and in both cases surface energy data collected for physical mixture samples comprised of amorphous and crystalline references fits the predicted response with good accuracy. Surface amorphous content of processed lactose samples is quantified using the calibration curve, and interpreted within the context of effective amorphous surface area. Data for bulk amorphous content is also utilized to generate a thorough picture of how disorder is distributed throughout the particle. An approach to quantifying surface amorphous content using dispersive surface energy is presented. Quantification is achieved by equating results to an effective amorphous surface area based on reference crystalline, and amorphous materials. © 2011 American Association of Pharmaceutical Scientists.


Kondor A.,Surface Measurement Systems Ltd. | Hogan S.A.,Teagasc
Food Chemistry | Year: 2017

Surface energetics of demineralised whey (DMW), skimmed milk (SMP), phosphocasein (PCN) and infant milk formula (IMF) powders were determined by inverse gas chromatography (IGC). All four milk powders were amphoteric in nature with the dispersive (apolar) component of surface energy dominating the specific (polar) contribution. PCN and IMF had the highest and lowest extent of surface heterogeneity, respectively. PCN also demonstrated the poorest functional properties of the powders examined. In contrast, IMF had excellent flow and rehydration properties. Thermodynamic work of cohesion was highest in PCN and may have contributed to inadequate rehydration behaviour. Glass transition temperature of IMF powder, determined by IGC, suggested a surface dominated by lactose. Surface heterogeneity provided a better indicator of functional behaviour than total surface energy. IGC is a useful complementary technique for chemical and structural analysis of milk powders and allows improved insight into the contribution of surface and bulk factors to functionality. © 2017 Elsevier Ltd


Burnett D.J.,Surface Measurement Systems Ltd | Khoo J.,Surface Measurement Systems Ltd | Naderi M.,Surface Measurement Systems Ltd | Heng J.Y.Y.,Imperial College London | And 2 more authors.
AAPS PharmSciTech | Year: 2012

The aim of this study was to investigate the effect of processing route (i.e., quench cooling and ball milling) on the surface energy heterogeneity and surface chemistry of indomethacin (IMC). Recently developed inverse gas chromatography (IGC) methodology at finite concentrations was employed to determine the surface energy distributions of crystalline, quench cooled and milled IMC samples. Surface properties of crystalline and processed IMC were measurably different as determined by the IGC and other conventional characterization techniques: differential scanning calorimetry and powder X-ray diffraction. Quench cooled IMC was in fully amorphous form. Milled IMC showed no amorphous character by calorimetric or X-ray diffraction studies. It was demonstrated that both processed IMC samples were energetically more active than the crystalline IMC. In particular, milled IMC exhibited a relatively higher dispersive surface energy and higher surface basicity (electron donor capability). This may be attributed to the creation of surface defect sites or exposure of higher energy crystal facets during the milling process. This study confirms that processing route has notable influence on the surface energy distribution and surface acid-base character. IGC was demonstrated as a powerful technique for investigating surface properties of real-world, heterogeneous pharmaceutical materials. © 2012 American Association of Pharmaceutical Scientists.


Carne-Sanchez A.,Catalan Institute of Nanoscience and Nanotechnology | Stylianou K.C.,Catalan Institute of Nanoscience and Nanotechnology | Carbonell C.,Catalan Institute of Nanoscience and Nanotechnology | Naderi M.,Surface Measurement Systems Ltd. | And 3 more authors.
Advanced Materials | Year: 2015

A one-step, alternative, rapid, and scalable spray-drying (SD) synthesis of metal-organic frameworks (MOF)@polymer composites with enhanced hydrolytic stabilities was reported. SD was used to encapsulate preformed MOF crystals in a polymeric matrix to generate microscale MOF@polymer spheres. For proof-of-concept Hong-Kong University of Science and Technology-1 (HKUST-1) was chosen as the water-sensitive MOF, and polystyrene (PS) as the organic polymer. The synthesis of HKUST-1@PS began with preparation of a stable colloidal suspension of HKUST-1 crystals and a solution of PS in dichloromethane (DCM). This mixture was atomized using a two-fluid nozzle. After 40 min of continuous spraying, 1.7 g of a blue powder was recovered. The sample was then washed with ethanol and dried at 120°C under vacuum. This product was analyzed through field-emission scanning electron microscopy (FESEM), which indicated that it comprised smooth microspheres of HKUST-1@PS composites and did not contain any free HKUST-1. X-ray powder diffraction (XRPD) analysis of these spheres revealed a perfect match with the HKUST-1 pattern. The exclusive presence of microspheres and the match in XRPD patterns evidenced that HKUST-1 crystals were indeed entrapped within the polymeric matrix of PS.


Moghaddam S.,University of Illinois at Urbana - Champaign | Pengwang E.,University of Illinois at Urbana - Champaign | Jiang Y.-B.,Sandia National Laboratories | Garcia A.R.,Surface Measurement Systems Ltd | And 5 more authors.
Nature Nanotechnology | Year: 2010

Proton exchange membrane fuel cells have the potential for applications in energy conversion and energy storage, but their development has been impeded by problems with the membrane electrode assembly. Here, we demonstrate that a silicon-based inorganic-organic membrane offers a number of advantages over Nafionthe membrane widely used as a proton exchange membrane in hydrogen fuel cellsincluding higher proton conductivity, a lack of volumetric size change, and membrane electrode assembly construction capabilities. Key to achieving these advantages is fabricating a silicon membrane with pores with diameters of ∼ 5-7nm, adding a self-assembled molecular monolayer on the pore surface, and then capping the pores with a layer of porous silica. The silica layer reduces the diameter of the pores and ensures their hydration, resulting in a proton conductivity that is two to three orders of magnitude higher than that of Nafion at low humidity. A membrane electrode assembly constructed with this proton exchange membrane delivered an order of magnitude higher power density than that achieved previously with a dry hydrogen feed and an air-breathing cathode. © 2010 Macmillan Publishers Limited. All rights reserved.


Lyn M.E.,U.S. Department of Agriculture | Burnett D.,Surface Measurement Systems Ltd. | Garcia A.R.,Surface Measurement Systems Ltd. | Gray R.,Surface Measurement Systems Ltd.
Journal of Agricultural and Food Chemistry | Year: 2010

Two obstacles for biopesticide commercialization, long shelf life and reliable efficacy, are both affected by moisture availability. Three biopesticide delivery systems, TRE-G, PEC-G, and PESTA, were analyzed by dynamic vapor sorption analysis. The objective was to investigate the moisture sorption profile of each system in air at 25 °C and a relative humidity (RH) ranging from 0 to 90%. The formulations sorbed up to 12.7% moisture. In rehydrating from 0.00 to 90% RH, TRE-G and PEC-G were ≥63% and ≥58% faster than Pesta, respectively. In losing moisture from 90 to 0.00% RH, Pesta was 3.4 and 2.3 times slower than TRE-G and PEC-G, respectively. The GAB model was inadequate for describing moisture sorption, but the Young and Nelson model showed good correlation (r> 0.990) for all three formulations. Moisture distribution for all formulations was obtained. The implications of the findings as they relate to shelf life and dew period requirements of biopesticides are discussed. © 2010 American Chemical Society.


Smith R.R.,Imperial College London | Williams D.R.,Imperial College London | Burnett D.J.,Surface Measurement Systems Ltd. | Heng J.Y.Y.,Imperial College London
Langmuir | Year: 2014

A computational model to predict the relative energy site contributions of a heterogeneous material from data collected by finite dilution-inverse gas chromatography (FD-IGC) is presented in this work. The methodology employed a multisolvent system site filling model utilizing Boltzmann statistics, expanding on previous efforts to calculate "experienced energies" at varying coverage, yielding a retention volume distribution allowing calculation of a surface free energy distribution. Surface free energy distributions were experimentally measured for racemic ibuprofen and β-mannitol powders, the energies of each were found in the ranges 43-52 and 40-55 mJ/m2, respectively, over a surface coverage range of 0-8%. The computed contributions to surface energy values were found to match closely with data collected on macroscopic crystals by alternative techniques (±<1.5 mJ/m 2). © 2014 American Chemical Society.


Grant
Agency: GTR | Branch: Innovate UK | Program: | Phase: Smart - Development of Prototype | Award Amount: 125.40K | Year: 2016

In our modern world, many classes of important materials such as pharmaceuticals, foods, polymers, catalysts and nanomaterials will absorb molecules such as water in the air, otherwise known as humidity. Indeed the manufacture, performance and stability of these materials is often dependent on this sorption behavior. Surface Measurement Systems has pioneered the development of scientific instruments for use in academic and industrial laboratories throughout the world for measuring the sorption behavior of materials based on sample mass changes: the so called gravimetric sorption method. This project will lead to the development of a new class of gravimetric sorption analysers which will allow experiments to be performed using either gas or vapour phase molecules for the first time, as well as allowing for multiple gas phase species to be analysed simultaneously. Combined with a new generation of microbalances for measuring the mass changes, these new sorption analysers will meet the more challenging and diverse needs of academic and industrial researchers, and will represent the new gold standard in gravimetric materials characterisation and are certain to be sought by leading researchers in laboratories throughout the world. Key applications for the use of these instruments will include the development of new materials for carbon capture, materials for separating methane from biogas as well as the development of the new catalysts and pharmaceuticals.


Grant
Agency: GTR | Branch: Innovate UK | Program: | Phase: Smart - Proof of Concept | Award Amount: 100.00K | Year: 2015

One of the most important methods currently available for characterising the surface properties of powders and porous materials is their ‘Brunauer–Emmett–Teller’ (BET) surface area which is determined using a gas adsorption isotherms, normally using nitrogen [1]. Such isotherms also provide key information on the pore structure, surface chemistry and morphology of powders. So utilitarian has become this laboratory technique that there are probably worldwide over 50,000 of these BET instruments in daily laboratory operation. However, these systems cannot be used to study monolithic thin film samples. The characterisation of such thin films is an area of increasing importance for semi-conductor, nano-porous films, graphene, catalysts and photo-voltaic materials to name but a few important industrial applications. The ability to study the surface properties and structures of these classes of materials is key to both their development and their future commercialisation. This project will evaluate the technical feasibility of determining gas and vapour adsorption isotherms on thin film substrates with surface areas of only a few square millimetres using a novel ellipsometric adsorption instrument. This instrument would allow a range of surface properties of monolithic thin films to be determined for the first time routinely including surface area, surface energy, surface heterogeneity, surface diffusion, surface reactivity and surface porosity. Such property measurements are key to the development of many classes of new nano-structured thin film materials. Such a successful development would offer the scope of commercialising Adsorption Ellipsometer as a major new research tool for the development of thin film materials.

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