Light transmittance is one of the key parameters for evaluating the optical properties of resin solutions, which reflects the solution's ability to transmit light at specific wavelengths. In industries such as coatings, adhesives, and polymer materials, the light transmittance of resin solutions directly affects the transparency, color, and appearance quality of the final product. As a classic optical analysis instrument, UV-Vis spectrophotometer can quickly and accurately determine the light transmittance of resin solutions in the ultraviolet and visible light bands, providing reliable data support for process control and quality evaluation.
Principle of determination
UV-Vis spectrophotometers are measured based on Lambert-Beale's law. When a beam of parallel monochromatic light passes through a homogeneous, non-scattering resin solution, the absorption of light by the solution is directly proportional to the concentration of the solution and the length of the optical path. Light transmittance (T) is defined as the light intensity (I) and incident light intensity (I) of the transmitted solution0) is usually expressed as a percentage. The relationship can be expressed by the following formula:
T = (I / I0) × 100%
At the same time, there is a logarithmic relationship between absorbance (A) and light transmittance:
A = -log10(T/100) = log10(I0/I)
In the actual measurement, the instrument directly calculates and outputs the light transmittance value by comparing the light signal of the sample cell with the reference cell (usually containing pure solvent).
Instruments and reagents
Assays are performed using UV-Vis spectrophotometers with wavelength ranges of 190-1100 nm, equipped with matching quartz or glass cuvettes. Key preparations are as follows:
| Instrument calibration | Boot up to warm up, perform baseline correction and wavelength accuracy verification |
| Cuvette selection | Quartz cuvettes are used for UV measurements, and optical glass cuvettes are used for visible regions |
| Solvent treatment | Choose the appropriate solvent (e.g., deionized water, alcohol, ketone) according to the resin type, and ensure that its light transmittance meets the requirements within the measured wavelength range |
| Sample preparation | The resin is evenly dissolved in the solvent to avoid bubbles and suspended solids, and filtered or centrifuged if necessary |
Assay steps
A standardized assay process helps to obtain reproducible data, with key steps including:
| Background scanning | Baseline recording is performed at the full wavelength or selected wavelength range using pure solvent as a reference |
| Sample loading | Inject the resin solution into the cleaning cuvette, wipe the outer walls, and place it in the sample chamber |
| Parameter settings | Set the scanning wavelength range, data interval, and measurement mode (transmittance mode) |
| Measurement execution | Start the scan and record the transmittance spectrum or the transmittance value at a specific wavelength |
| Repeat verification | The same sample was measured at least three times in parallel, and the mean and standard deviation were calculated |
Influencing factors
The following factors need to be controlled during the measurement process to ensure accurate and reliable data:
Solution concentration and optical path: Too high resin concentration may cause the absorbance to exceed the linear range of the instrument, and it is recommended to adjust the concentration to make the light transmittance in the range of 20%-80%. The cuvette light path is usually 10 mm, and a shorter light path can be selected for high-absorption samples.
Solvent matching: The reference cell solvent must be exactly the same as the sample solvent to eliminate background interference from solvent absorption.
Wavelength selection: For colorless resin solutions, the light transmittance in the visible light region (e.g., 400-800 nm) can be measured; If the solution contains UV absorbing components, it needs to be extended to the UV region. Commonly reported wavelengths are 450 nm, 550 nm, or 660 nm, as determined by industry practice or product standards.
Instrument maintenance: Clean the cuvette regularly, check the stability of the light source and the performance of the detector, and conduct interim verification according to the measurement procedures.
Data interpretation
The results of the assay are usually expressed as a transmittance spectrum or a transmittance value at a specific wavelength. Higher light transmittance indicates better transparency of the resin solution with fewer impurities or undissolved substances. This data can be used to:
1. Monitor the stability of the resin synthesis or purification process;
2. Evaluate solvent quality or resin compatibility;
3. As one of the bases for product classification or conformity judgment.
It should be noted that there are differences in the requirements for light transmittance between different resin systems or application scenarios, and relevant material specifications or customer agreements should be referred to when interpreting.
Summary
The determination of light transmittance of resin solution by UV-Vis spectrophotometer is an analysis method with simple operation and objective results. Through standardized sample preparation, instrument operation and data processing, key parameters reflecting the transparency of the solution can be effectively obtained, and technical support can be provided for production quality control and product development. In practical applications, combining specific resin characteristics and industry standards, rationally selecting measurement conditions and continuously optimizing methods can help improve the practicability and comparability of measurement results.
References
1. Chemical Industry Press, "Analytical Instrument Use and Maintenance", 2020.
2. ASTM E275, Standard Practice for Describing and Measuring the Performance of UV-Vis Spectrophotometers.
3. National Standardization Administration of China, GB/T 23978, "Determination of light transmittance of liquid dyes".