Modified data handling for rapid low‐field nuclear magnetic resonance characterization of lyotropic liquid crystal composites

• Published in: Journal of surfactants and detergents Vol. 2; no. 4; pp. 515 - 521
• Main Author: Nadakatti, Suresh M.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01-10-1999; Springer Nature B.V
• Subjects: Composite materials; Crystals; Data acquisition; Data analysis; Data processing; Design standards; Detergents; Free induction decay; Handling; Liquid crystals; Liquid phases; Methods; multiphase composites; NMR; Nuclear magnetic resonance; Phase composition; soap phases; Spectrometers; Systems analysis; T2 relaxation; wideline NMR
• ISSN: 1097-3958; 1558-9293
• DOI: 10.1007/s11743-999-0100-9

A refined nuclear magnetic resonance (NMR) technique was developed to determine the relative volumetric proportions of various phases present in lyotropic liquid crystal (LLC) composites such as soap/detergent bars. Conventionally, the FID (free induction decay, referred to hereafter as Method 1) technique is used for analysis of these systems. This technique is suitable only for composites containing a high concentration of solids and liquid crystals. Method 1 gives erroneous results for composites with a high proportion (>10%) of isotropic liquid phase (L1). The procedure currently practiced (Method 2) for analyzing systems containing >10% L1 entails a considerable amount of experimental and analysis time and involves subjectivity in data analysis. Typically, the phase characterization of the composite using conventional low‐field NMR techniques takes more than 1 h. Furthermore, the hardware and data acquisition features of currently available conventional low‐field NMR spectrometers are inadequate for accurate estimation of relative phase volumes in LLC composites. We developed a modified data‐handling technique (FID—Carr‐Purcell‐Meiboom‐Gill technique, or FIDCPMG technique) which enabled rapid phase characterization of LLC composites and minimized subjectivity while analyzing the data. The standard design of a conventional low‐field NMR spectrometer was upgraded by incorporating a high‐power transmitter and a fast digitizer. The phase composition of four model LLC composites (with L1 percentages varying from 7 to 90%) was determined using FIDCPMG technique and was compared with results from conventional techniques. Phase composition of the LLC composite could be determined in less than 5 min.