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Measuring the composition of paper

Researchers at NIST have developed a new technique for analyzing the composition of paper. The technique measures the response of water molecules in the paper to an alternating electric field. Water is a polar molecule, meaning one side is positively charged and the other is negatively charged. When placed in an electric field, the molecule aligns to the direction of the field. If the field alternates, the molecule rotates so that its polarization exactly follows the direction of the changing field. However, the water molecules in paper are surrounded by organic polymers. These polymers inhibit the rotation of the water. In an alternating electric field, the polarization of the molecule now lags behind the direction of the field. By measuring this lag, researchers can determine the composition of the paper.

February 2019 • NIST • • Tagged: Animation