In philosophy|lang=en terms the difference between sentimentalism and sensationalism

is that sentimentalism is (philosophy) a view according to which morality is somehow grounded in moral sentiments or emotions while sensationalism is (philosophy) a theory of philosophy that all knowledge is ultimately derived from the senses.

As nouns the difference between sentimentalism and sensationalism

is that sentimentalism is a liking for sentimental things while sensationalism is the use of sensational subject matter, style or methods, or the sensational subject matter itself; behavior, published materials, or broadcasts that are intentionally controversial, exaggerated, lurid, loud, or attention-grabbing especially applied to news media in a pejorative sense that they are reporting in a manner to gain audience or notoriety but at the expense of accuracy and professionalism.